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How Do I Fix My Home Security Alarm? (Top Repair Tips)

Eugene is a qualified control/instrumentation engineer Bsc (Eng) and has worked as a developer of electronics & software for SCADA systems.

Does your home alarm keep going off for no reason? Learn how to troubleshoot and fix alarm system issues.

Does your home alarm keep going off for no reason? Learn how to troubleshoot and fix alarm system issues.

Troubleshooting and Repair for False Alarms in a Home Security System

A blaring sounder on a security alarm is annoying both for you and for those who live nearby. If you have good neighbors, they may keep an eye out for activity in the vicinity of your home when the alarm sounds. However, if false alarms occur regularly, it can be like a scenario from the story The Boy Who Cried Wolf and they may just ignore it!

This guide explains the basics of how alarms work and how sensors are wired. It also covers the various faults which occur in sensors resulting in nuisance activation of your alarm.

What Causes False Alarms?

  • Loose connections
  • Loop resistance outside the specified limits
  • A worn out backup battery in the panel
  • A misaligned or incorrectly spaced magnet
  • Rodents, birds, bats, spiders or other small animals may be triggering sensors, especially in lofts or outbuildings
  • Tamper strips on junction boxes may be tarnished and causing bad connections
  • Tampers on some sensors are badly designed and may only barely close the tamper switch in the sensor when the lid is replaced. Consider replacing the sensor
  • PIRs badly positioned and subject to nuisance trigger conditions

How Does a Burglar Alarm Work?

Alarm systems for homes come in two different formats:

  1. An alarm panel with an integrated display and keypad to which sensors are hardwired or linked by radio (known as wireless or radio frequency (RF) sensors)
  2. Alternatively sensors may be wired or connect wirelessly to a box without a display or keypad, hidden away out of reach of burglars, so that it can't be tampered with. A second advantage of this is that wiring can be hidden out of view and a smaller more discrete keypad can be mounted on a wall. All the electronics, backup power, connection terminals, autodialler/GSM modules are kept inside this box. The user then interacts with the box via a remote wired or wireless keypad mounted on a wall.

A microcontroller (which is a type of microprocessor) on the circuit board in the alarm panel/alarm box runs a software program which scans the sensors regularly. The program will generate an alarm if it thinks a sensor has been activated and an intruder has entered the building.

What Are the Components of an Alarm System?

Learning about the different parts of the alarm system and their functions can help you troubleshoot issues.

Alarm Panel

The alarm panel itself may have a rudimentary display consisting simply of LEDs, or a more fancy LCD display may be provided which gives textual information about the status of the alarm, which zone an alarm occurred in, error codes etc.
have a keypad for entering passwords and commands.

Several remote auxiliary keypads without displays may also be provided for arming/disarming the alarm in the vicinity of additional exterior doorways. An attempt at entering an alarm code at the panel (if the sensors have been bypassed) will also trigger a "countdown" of the alarm.

Alarm panels can be wired, wireless or a hybrid. As a replacement panel in an existing system, the latter type allows pre-existing wired zones to be connected and also additional wireless sensors which have the obvious advantage of not requiring possibly ugly surface wiring.

Backup Battery Power

An alarm panel is usually provided with backup power by a 12 volt lead acid battery. In less expensive systems, nickel metal hydride (NiMh) AA cells may be used. The backup battery maintains power to the alarm panel, sensors and sounder in the event of a power cut or when an intruder cuts mains power to the panel from outside a building.


An external sounder operates when the alarm is triggered. Older systems used electromechanical bells. Most modern systems use electronic piezoelectric transducers in the sounder. Sounders are powered by solar panels or a cable from the alarm panel. A backup battery is often installed in the sounder so that it still works if a burglar cuts the alarm cable (in additional to signals, this cable also provides power for powering the sounder and charging the backup battery


These devices detect opening of windows or doors, body heat from intruders walking around a room, stepping on mats, or attempts to break glass in windows and doors.


Either integrated into the alarm panel or a separate wired or wireless unit.

Block Diagram of a Basic Security Alarm System

A basic 3 zone alarm system. 1 or more sensors are connected in series to each zone

A basic 3 zone alarm system. 1 or more sensors are connected in series to each zone

What Are Alarm Zones?

An alarm panel usually has several zones to which sensors are connected. The idea of separate zones is so that when arming the alarm, sections of the installation can be included/excluded from being armed. To set the alarm, a button on the panel corresponding to part arm or full arm is pressed by the user. Alternatively a series of buttons is pressed on the keypad (e.g. 0#4 or 0#3). There are normally three basic arming modes for a panel:

Full Arm

All zones are armed when a house is vacated.

Part Arm

The alarm is armed with some zones excluded. These zones can be preset when the alarm is programmed by the user/engineer so that they don't have to be picked when arming.

Consider this scenario:

  • Exterior doors on zone 1
  • Downstairs windows on zone 2
  • Upstairs windows on zone 3
  • PIR sensors to detect movement on zone 4

Part arm is used typically to set an alarm at night

In this setup, zone 4 PIRs could be excluded to allow an occupant to wander around the house, and zone 3 could be disabled to allow upstairs bedroom windows to be left open in hot weather.

Inhibit Zones

The user chooses the zones to be excluded as they arm the panel.

Entry/Exit Zones

An entry/exit zone is reserved for genuine entry to the building via a doorway. This zone has a delay associated with it before the sounder operates, allowing a password to be entered to disarm the panel.

More sophisticated entry alarms for larger buildings will have a greater number of zones and the ability to identify activation of individual sensors, possibly indicating the sensor location on a computer screen mimic, depicting the floor plan of the building.

On a wired system, one or more sensors can be connected in series to each zone, known as "daisy-chaining". The disadvantage of daisy-chaining is that if one sensor develops a fault and contacts stay stuck open, the zone has to be omitted during arming, making the other sensors useless until the fault is rectified. Another disadvantage is that the specific sensor in the chain that triggered an alarm can't be narrowed down and only the zone can be identified.

Many modern alarm panels have zones which can be programmed to respond in a desired way to sensors. So a zone can be used as a standard alarm zone, a 24 hour tamper circuit, panic circuit, entry/exit zone, fire alarm zone etc.

When an alarm occurs or the panel cannot be armed (for example due to a window left open), the panel normally indicates the problem zone. Some panels can be setup to ignore the zone when armed.

Tamper Circuits and Panic Buttons

Tamper Circuit

A tamper circuit detects an intruder interfering with alarm system wiring even when it is not armed. This is sometimes called a 24 hour circuit. Panels may have a single tamper circuit or a dedicated tamper circuit for each zone.

Panic Button

A panic button circuit and panic buttons may be included. When a panic button is pressed, the external sounder activates. Panic buttons can be located near doorways, in bedrooms etc.

How Do Burglar Alarm Sensors Work?

Sensors are electronic/electrical devices and in the context of security alarms, they either detect entry of an intruder into a building via a window or door, or directly detect the intruders presence. They are small modules which contain microswitches which are normally closed. The switch contacts are normally "volt free". This means that they are isolated from the electronics of the sensor, so that they can be connected to any external voltage source.

When a sensor is activated, the microswitch opens and breaks a circuit. The alarm panel detects this and activates an external wall and internal sounder. The panel may autodial a phone number or send an SMS text message to a cell (mobile) phone. Some alarm systems are monitored by an alarm company to which a subscription is paid.

Typical Sensors

  • Contacts on windows and doors These contain a tiny reed switch enclosed in a small glass tube within the body of the sensor. The switch is kept closed by a nearby magnet.
  • Shock sensors Used for detecting someone attempting to break glass or otherwise using impact force to attempt to gain entry. These may also incorporate magnetic contacts.
  • PIR Sensors These detect the body heat from an intruder as they walk past the sensor.
  • Microwave Sensors Like PIR sensors, they detect intruders but have certain advantages over them.
  • Pressure Mats Detect intruders stepping on a floor.

Wired and Wireless Sensors

Wired sensors are powered by the alarm panel, typically using a pair of cores in the cable to provide a 12 volt supply.

Wireless sensors are usually powered by non-rechargeable lithium ion 12 volt batteries with a lifespan of several years. Sensors communicate with the panel over a low power radio link. New sensors are normally "added" to an alarm system after they are physically installed and the panel IDs the device so that it can subsequently read its alarm status. Usually each wireless sensor will be on a separate logical zone.

What Is a Tamper on an Alarm System?

A basic wired alarm system uses 6 core cable for connection to sensors, 1 pair for power, 1 pair for tamper and 1 pair for the microswitches in sensors which open when the sensor is triggered. Sensors are typically powered by 12 volts DC. If several sensors are used per loop, the microswitches can be wired in series. One core of the cable travels outwards from the alarm panel to all the sensors, and another core of the cable returns to the panel to complete the circuit, similarly for the tamper circuit.

A tamper or 24 hr circuit consists of a pair of tamper cores in the alarm cable and momentary tamper switches in sensors, the alarm panel, junction boxes and sounders. These switches are maintained in a closed position by lids/covers on sensors and other components of the system. If anyone removes a lid while the alarm is unarmed, or cuts a cable, (cutting through the pair of tamper wires) a warning sounder will indicate this situation (but the exterior sounder may not activate). If the alarm is armed, the main sounder will activate.

Some sensors, e.g. door and window contacts don't have any integrated electronics or tamper switches and so only 2 cores of the alarm cable are required.

Wiring of alarm contacts in sensors to the control panel (power and tamper not shown). In this example, the contacts are "daisy chained" or linked together in series.

Wiring of alarm contacts in sensors to the control panel (power and tamper not shown). In this example, the contacts are "daisy chained" or linked together in series.

This PIR sensor has 3 pairs of terminals. Alarm contacts are normally closed (n/c) and open on activation .Tamper contacts are n/c and open when lid is removed.

This PIR sensor has 3 pairs of terminals. Alarm contacts are normally closed (n/c) and open on activation .Tamper contacts are n/c and open when lid is removed.

Wiring Two Sensors in Series

Sensors can be wired in series on a zone. A core of the cable for both tamper and alarm contacts loops back from the last sensor in the zone to the alarm panel. An EOL resistor may be included in series at the last sensor.

Sensors can be wired in series on a zone. A core of the cable for both tamper and alarm contacts loops back from the last sensor in the zone to the alarm panel. An EOL resistor may be included in series at the last sensor.

Wiring 2 Door/Window Contacts in Series

Door/window contacts can be connected in series. They don't require power and sometimes don't have tamper microswitches. An EOL resistor may be included in series at the last sensor.

Door/window contacts can be connected in series. They don't require power and sometimes don't have tamper microswitches. An EOL resistor may be included in series at the last sensor.

End of Line (EOL) Resistors and Single End of Line Wiring

Older alarm systems as described above had zone loops which were either closed circuit when no sensors were triggered or went open circuit when a sensor activated. This resulted in a low voltage or high voltage respectively at the control panel.

The flaw in this system was that a burglar could short out zone wiring "upstream", between panel and sensors, effectively bypassing them. Then at a later stage they could attempt a break in. Because the zone was shorted, when a door/window contact opened or a sensor activated, it would be undetected by the control panel.

Newer alarm systems are made more secure by adding a resistor, typically about 5k, at the end of the loop. This is known as an end of line (EOL) resistor and adds supervision to the loop by detecting shorted wiring. The panel now has 3 voltages it can possibly measure, high voltage with the loop open (due to a broken/cut wire, or a sensor activating), low voltage if the zone wiring is shorted by a fault/burglar, or an intermediate voltage in a non fault/non triggered scenario.

EOL resistors must be fitted at the last sensor in a loop so that the panel can detect when a burglar shorts the two alarm cores in a cable "upstream", that is on the panel side of wiring to sensors. If resistors are fitted in series with the loop at the panel, they cannot detect that this has occurred.

If only one resistor is used at the end of the zone, this is called single end of line wiring.

Fully Supervised Loop (FSL) and Closed Circuit Loop (CSL) Wiring

Basic alarm systems use 2 cores for sensors, 2 cores for tamper and 2 cores if needed for powering sensors. The problem is that a global tamper is used and this loops through all the zones on the panel. So if a burglar cuts a cable, this deactivates the tamper for all zones and potentially puts the system out of action until the break can be pinpointed.

Fully Supervised Loop wiring provides a separate tamper for each zone, so if a cable is cut or a loose connection occurs in the tamper circuit, only that zone will be out of action and also it's easier to trace the fault. An EOL resistor is used at the last detector plus in addition a resistor across the contacts of each sensor in the loop. This is called dual end of line wiring. The system can then differentiate between a no alarm condition, a tamper, or an alarm condition, using just 2 cores of cable for both contacts and tamper. A third core is needed if multiple sensors are daisy chained together.

Door / Window Contacts

These come as two parts, the contact part and a magnet. The contact part consists of a small plastic module containing a reed switch (a miniature switch enclosed in a thin glass tube) which is mounted on the door jamb or window frame. The magnet part is fixed to the door, or window sash / casement so that it is close to the contact part when the door or window is closed. This keeps the reed switch in a closed state. When a window is opened, the magnet moves away from the contact and the reed switch opens.

Contacts don't require power and only 2 cores of a cable are required, however if 6 core cable is used, 2 unused cores in the cable can be used for powering additional sensors added to the loop at a later stage. Sometimes they don't have tamper contacts either, however 2 of the cores can be wired to tamper contacts in junction boxes or sensors, during modifications/upgrade to the system. Shock sensors and magnetic contacts are also available as a combined unit.

Magnets should be placed as close as possible to the contact part, within the specified spacing. If the gap is too large, a contact may stay closed ok for a period, but open if there are any vibrations, causing spurious alarms. Sometimes there is an arrow on the contact indicating which side should face the magnet.

Window contact and magnet

Window contact and magnet

PIR Sensors

These sensors use an element sensitive to human body heat. When someone walks in front of the sensor, electronics in the device opens a microswitch which triggers an alarm.

PIR sensors have varying ranges and detection profiles over which they are sensitive. Usually they have near, far, and possibly intermediate zones through which an intruder must pass before triggering an alarm. Normally sensors are sensitive over at least a 90 degree sector, but omnidirectional versions are available.

Shock Sensors

Shock sensors are bonded to glass in a door or window or fixed to the frame. During setup, the sensitivity of the sensor can be set and the number of impacts which trigger an alarm. Some sensors are "intelligent" and can detect the sound of breaking glass. Shock and magnetic contact sensors can be combined into one unit.

Troubleshooting Sensors Which Don't Work or Cause False Alarms

There are several causes of false alarms or sensors which fail to operate:

  • Badly positioned PIR sensors
  • False triggering of shock sensors
  • Loose connections
  • Alarm contacts in sensors becoming faulty
  • Tamper switches becoming faulty
  • Voltage spikes on supply
  • Backup battery problems
  • Badly placed or damaged wiring

Remember you can use a shorting link at the terminals of the panel if you need to isolate any zones for testing purposes (e.g to test continuity of a loop) or to disable a zone. A short piece of insulated wire is ok. This allows the alarm to be used normally while testing.

What Causes False Triggering of PIR Sensors?

PIR sensors are triggered by movement of humans walking perpendicular to the sensor through its sensitive zones. If a sensor is mounted outdoors, it can also be triggered by cats or other large animals. Sensors are available which are only sensitive to human movement.

False Triggering can be caused by:

  • bats, birds, rodents, spiders or other small animals, especially if a PIR is located in an outbuilding
  • warm air currents if the sensor is pointing towards a radiator
  • draughts coming under doors
  • a sensor facing towards a window and picking up variations in heat caused by the sun. Sensors can't "see" through glass and have dual element sensors to make them insensitive to overall changes in sunshine level. However large changes in IR intensity caused by cloud movement could trigger a sensor if it faces out a window.

How Should I Position a PIR Sensor?

Ideally place sensors in the corner of a room, facing away from a window and any heat sources. Also it should be located so that intruders are likely to walk perpendicular to the device, through the sensitive zones, rather than towards it. It should also be mounted high enough on a wall and angled in such a way that intruders cannot crouch down and pass through a blind zone (i.e low and close to the sensor). See diagram below. Instructions provided with sensors normally provide diagrams outlining the regions of sensitivity.

Zones of Sensitivity for a PIR Sensor

A PIR is most sensitive to intruders walking perpendicular to the zones. If the sensor is angled incorrectly, an intruder could crouch close to a wall and not be detected.

A PIR is most sensitive to intruders walking perpendicular to the zones. If the sensor is angled incorrectly, an intruder could crouch close to a wall and not be detected.

Are Some PIR Sensors Better Than Others?

Newer sensors are less likely to cause false alarms. Consider upgrading to pet immune, dual-tech, dual or quad PIR types to lessen the chances of this happening.

False Triggering of Shock Sensors

This type of sensor can be subject to false alarms caused by hailstones hitting windows, or more likely skylights, birds seeing their reflections and banging on glass or even impact of heavy traffic on roads close to exterior walls. There may be a setting inside the sensor to reduce the sensitivity. Also the number of impacts required to trigger an alarm can usually be set and this may need to be increased.

Loose Connection Repair

Loose connections are always a cause of problems with any electrical or electronic device. When installing sensors, screws should be screwed down tightly on the cores of alarm cable, and ideally boot lace ferrules should be used to keep the strands of wires together.

Ferrules are crimped onto the ends of wire and prevent the fine strands of wire of from being damaged by screws of terminals. They also make it easier to remove and replace wires from terminals, and have a shroud to prevent inadvertent contact between loose strands of wire and adjacent terminals. Connections can also become corroded over time, especially in damp environments.

Boot lace ferrule

Boot lace ferrule

Checking the Loop Resistance

Alarms are triggered when a normally closed (NC) microswitch in a sensor, or a tamper contact goes open circuit. The resistance of a loop circuit (consisting of sensor contacts and loop wiring all connected in series) must be below an upper limit with all switches closed. This is usually 5 to 10 kilo ohms, but depends on the panel.

Also the resistance of the loop when a contact opens has a lower limit, in the range of 100 kilo ohms. To check the resistance of a loop, remove the two wires connected to the zone input at the alarm panel and connect the probes of a digital multimeter, set to the ohms range, to these two wires.

Resistance should typically be less than 100 ohms (or around 5k if an EOL resistor is fitted at the last sensor), but can rise if sensors are giving trouble or if you have many sensors connected in series and long cable runs. If the resistance is excessively high, several hundred ohms or greater, further investigation is necessary.

If you have an assistant, they can watch the meter and you can bridge the alarm contacts of each sensor in turn with a piece of wire. By a process of elimination, this will enable you to identify the problematic sensor.

Alternatively, you can go to each sensor in turn with the meter and measure the resistance across the alarm contacts. Remember that the loop must be disconnected from the panel, otherwise voltage will be present on the contacts, giving a false reading. Also PIRs and other sensors requiring power must be powered up for the contacts to operate.

See this guide for instructions on how to use a multimeter: How to use a digital multimeter (DMM)

Alarm Contacts in Sensors Becoming Faulty

Over time, the resistance of microswitches in sensors can increase. Ideally the resistance of a closed switch should be zero ohms, but this can become higher as switches age. If doors and windows are rarely opened, the reed switches in magnetic contact sensors can become "sticky" and fail to open, preventing the alarm from activating if an intruder breaks in. Another possibility is that the magnet can become weak, failing to keep the contact closed, especially if it wasn't placed close enough during installation. This can cause nuisance triggering, when e.g. vibration from wind or heavy nearby traffic is sufficient to shake the contact open.

To check the resistance, set your DMM to the ohms range and measure resistance between the screw terminals. The loop should be disconnected at the alarm panel to remove voltage from the terminals, and of course in the case of magnetic contacts, the magnet on the window or door should be adjacent to the contacts to keep the reed switch closed.

Set the DMM to the ohms range and measure resistance between screw terminals of contacts. The loop should be disconnected at the alarm panel to remove voltage from the contacts.

Set the DMM to the ohms range and measure resistance between screw terminals of contacts. The loop should be disconnected at the alarm panel to remove voltage from the contacts.

Tamper Switches Becoming Faulty

Tamper switches consisting of a spring operating a microswitch are used to detect someone removing the lid of a sensor or other components of an alarm system. An alternate style of switch consists of springy, nickel coated metal strips, pushed together when a lid is in place. These strips can tarnish over time, contributing to an increase in the loop resistance. This can produce false alarms as contacts expand and contract, and move relative to each other during hot or cold weather.

Contacts can be cleaned with a piece of fine wire / steel wool and then wiped with rubbing alcohol / IPA (Isopropyl Alcohol). Don't overdo it because the coating (It's either nickel or chrome) could be removed.

Sometimes sensors have tamper microswitches that are closed by a projection on the lid (often a small round piece of rubber) of the sensor when it is replaced. It can happen with badly made sensors that the rubber piece on the lid gets squashed over time and loses its springiness, so it doesn't put enough pressure on the microswitch. The symptoms are a sensor that generates a tamper when knocked (and possibly may do so if there is nearby heavy traffic causing vibration).

Alarm panel lids can also cause tamper faults, so check they are seated properly when replacing.

Tamper Contacts in a Junction Box

Tamper contacts in a junction box (the outer casing has been removed)

Tamper contacts in a junction box (the outer casing has been removed)

Clean with fine wire wool and IPA

Clean with fine wire wool and IPA

Voltage Spikes on Supply

Voltage spikes on your mains supply are caused by disturbances such as heavy loads being switched on and off in the locality, generators coming on and going off line, switching activity in substations and lightning strikes. These spikes can trigger false alarms. Your alarm is likely to be powered directly via a cable from the electrical panel in your home or via a spur from a cable via a fused connection unit. A surge filter may give some protection from false alarms caused by spikes injected into the power supply of the alarm panel.

Backup Battery Problems

A lead acid or NiMh battery is used to keep an alarm alive in the event of power failure due to an interruption of your supply or deliberate cutting of power by an intruder. These batteries have a limited lifespan of 3 to 5 years. As a battery ages, its voltage can fluctuate, injecting noise spikes into the system.

When a battery nears the end of its life, its capacity decreases and the length of time it can maintain backup if the power fails or is cut by by a burglar decreases. The sounder on your exterior wall also may have an internal backup battery. Not all sounders do however, and you should consider upgrading if yours doesn't. If a burglar cuts the cable to a sounder without a backup battery, it's rendered useless. These batteries also have a limited lifespan.

Badly Placed or Installed Wiring

If wiring is run adjacent to power cables, voltage spikes can be coupled directly into the alarm cables. During installation, staples or clips may have cut through alarm cable. This can cause problems later as cores get shorted out. Also if you have had workers in your home doing renovations, make sure they haven't dislodged or damaged sensors, cables etc.

Buttons Not Working on the Keypad

Although older alarm panels may have keys which are actually push buttons (like what used to be used on computer keyboards), newer keypads are usually membrane type. These have "contacts" printed as pads onto a PCB, and conductive rubber pads on a moulded flexible membrane. When a key is pressed, the rubber pads press against the PCB and complete a circuit.

This type of keypad is also used on TV remote controls. Over time, the conductive rubber pads lose their conductivity, however they can be repaired. See this article: How to Repair a Keypad or Remote Control With Kitchen Foil

The keypad of an alarm is similar to this membrane keypad from a remote control

The keypad of an alarm is similar to this membrane keypad from a remote control

The conductive pads on the membrane make contact with copper contact pads on the PCB

The conductive pads on the membrane make contact with copper contact pads on the PCB

GSM Units for Sending SMS Messages

A GSM module can be optionally fitted externally or internally in some alarm panels so that SMS messages can be sent to a cell phone (mobile phone). These messages are typically notifications of alarm activation, faults and confirmation of arming/unsetting of the panel.

A GSM unit also allows you to remotely arm the panel, disarm it and reset it when an alarm occurs. These modules have a SIM card and credit on the account may be automatically topped if you have a subscription with an alarm company. If you use your own SIM, obviously you need to remember to top up before credit expires so that the GSM unit continues to function.

How Often Should Burglar Alarms Be Serviced?

Generally once a year. However if you get a discount on your home insurance, there may be further stipulations, so check your policy.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: My burglar alarm sensor keeps making a clicking noise, how do I stop this? The sensor is a KX15DT Pyronix sensor.

Answer: If the sensor has a mechanical relay, it can make a clicking noise when the sensor detects movement. If it's continually clicking without movement, it may indicate the sensor is faulty.

Question: I only have six sensors installed on my burglar alarm, but tonight a seventh sensor went off three times. I don’t know what triggered it, or where the seventh sensor came from. In the end, I deleted that sensor. How is the alarm doing that?

Answer: It could be a shorting at the panel link on that zone is loose.

Question: I have a Scorpion Z6 alarm installed 2000. I want to repaint the bell housing which is rusted. How do I turn off the tamper alarm to remove the cover?

Answer: I can't find a manual for this specific alarm, but if I'm doing any maintenance on my bell or panel, I tie up the tamper spring. This spring usually makes contact with the cover of the bell and pushes against a microswitch on the PCB and keeps it closed. I use a piece of wire or string and tie it to any convenient hole, projecting a piece of plastic or similar in the housing. Sometimes I use a crocodile clip or clothes peg and clip this onto an edge and tie the wire to this.

Question: This morning my Honeywell Accent G4 alarm went off but read no faults on the keypad, so I had to get out my ladders and disconnect the battery in the siren, the battery in the main panel and pull the fuse. On closer inspection of the panel the only normal resistor has burnt out, all others are resistors. Any idea why this resistor in my Honeywell Accent G4 Alarm would have burnt out?

Answer: Sounds like there was a short somewhere on the board. Logic circuitry/the microcontroller on board will work on 5 or 3 volts, powered by a voltage regulator. Wired sensors run on 12 volts, again sourced by a voltage regulator which would probably source 1 or 2 amps.

The resistor here seems to be in the power /supply battery section. If the resistor has burnt out, chances are some of the other electronics became faulty and caused this to happen, so even if you replace it, it may blow again.

Question: I got message code 403 'Kitchen open' on my alarm panel. The PIR sensor also keeps flicking. Also, when I try to set the alarm, it will not set as the code message appears. Can you guide me on how to fix this?

Answer: You need to source the manual for the specific brand of control panel to see what the "403" code refers to. If the sensor is activating, it could be due to faulty wiring/loose connections, or a faulty sensor if there was no problem previously. Another possibility is a low battery if the system is wireless, but it should tell you this.

Question: I have a wired door sensor that stopped working but allowed the alarm to be armed without bypassing a zone. How is this possible?

Answer: Sounds as though it has failed and the contacts are staying closed. If it's faulty with the contacts stuck open, then it would prevent the system from being armed.

Question: My keypads are displaying each zone starting with zone 1, zone 2, zone 3, etc. in a continuous loop, even though no batteries are low. It is just continually cycling through, displaying each zone. Do you know what caused this? I turned off the power, and it took a few hours, but the same thing started up again.

Answer: Sounds as if the alarm is in some form of polling mode, checking all the zones. Sorry, I don't know what could be causing this, so it's best to call an alarm service technician to resolve the problem.

Question: My PIR is showing active all the time and I cannot activate my alarm. What can I do?

Answer: If the PIR is wired, it could be due to loss of voltage caused by a blown fuse, loose connection or broken wire. On a wireless system, the battery may simply be flat although I would think your panel should indicate this.

Question: My house alarm keeps sounding the internal sounder, and it happens every day. We have checked the spring, and it seems to be working fine, so I don't know what to do. My alarm is a C&K Securitech 800L. Do you know what I can do?

Answer: If it is just the internal sounder, the chances are that it's a tampering problem. (This should be indicated on the display, or an LED will indicate either a "24 hr" or "tamper").

A tamper fault can be caused by loose connections in sensors, voltage spikes on power lines or bad connections in junction boxes. These sometimes have springy metal strips that are closed when the lid is replaced. Resolving the problem is basically a process of elimination, making one change at a time and seeing if stops the fault occurring.

Page 3 of this manual indicates how to deal with tamper faults:

Question: We have an existing Pyronix alarm panel. Is it OK to use an external sounder from a different manufacturer? I like the look of an external sounder from Texecom, because it is IP65, rather than IP44 and the box is exposed to prevailing weather. I have already replaced PIRs and door contacts, no problem. Kind regards Lindsay

Answer: There shouldn't be an issue and most sounders run on 12 volts. Connections can be slightly different between panel and sounder, but often a wiring diagram comes with the sounder showing how it should be connected to different panels. The people on the UK security installers forum were very helpful, knowing more about the details of different systems than I do and I got advice from them on how to connect my new sounder a couple of years ago.

This is the forum:

Question: Hi, an alarm sensor in my dining room was noisy. It sounded like dial-up internet, so I removed the front box and pulled the red wire out. I'm guessing it was the power wire. Is this dangerous?

Answer: It sounds odd. PIR sensors have a relay, which clicks when it opens/closes, but if the electronics have gone wonky, it could be switching on and off rapidly, producing a buzzing or whining sound. Sensors are normally powered by six core cable, one pair for 12 volts power, one pair for the alarm contacts and the remaining pair for tamper. However, this cable is light gauge. If you're referring to the connection box for the alarm panel, this will be fed by mains power, the colours for mains/hot depending on your country. The red may be power if it's an old installation in the UK (old power cable cores were red and black for live and neutral respectively). Might be a good idea to get an alarm installer or electrician to check it out.

Question: Spring switch appears to be operating ok. How do you get rid of a tamper lid fault?

Answer: If the system is wired and you have a single tamper loop, the fault could occur at any of the sensors or junction boxes on the loop or the sounder. If there's an individual tamper for each zone, this narrows things down. Check the spring is being pushed down entirely and isn't being pushed awkwardly off to one side when the lid closes. Check wires are pushed fully into terminals and they are screwed down tight. Junction boxes usually have springy metal contacts that implement the tamper. A piece of plastic on the lid pushes the contacts together when the lid is replaced. Make sure there are no wires in the way preventing the lid from sitting properly on the box.

If your alarm identifies which sensor is causing the problem and you have a multimeter, you can remove the tamper wires from the screw terminals and check that the meter indicates continuity when the switch is closed. For a wireless alarm, again make sure the lid is sitting properly when replaced and also that batteries in the sensor/sensors are ok.

Question: The alarm went off and the keypad was completely dead. It stopped after about 10 minutes and the pad and all the sensors are dead, but the input light is on at the power supply. Is it a fuse problem or what?

Answer: If there are any LED indicators on the sensors/keypad and they aren't lit up, it sounds like a fuse could be blown, or the power supply feeding the sensors may be faulty.

Question: As soon as I enter my house, the alarm goes off; there's no time to disable it. Why does this happen?

Answer: The settings may have become corrupted on the alarm. Usually these are set in engineer mode on the panel. Consult the manual for the panel to see what codes you have to enter to change the entry time, and also set the zone for the external door as a walk through zone if necessary.

Question: Can I disconnect a door sensor on my burglar alarm system?

Answer: You can exclude it when arming your alarm. If it's an external door, you won't, of course, get an audible countdown warning when you enter through that doorway.

You can also bypass the sensor by using a wire link across the contacts.

Question: When I key my code into the keypad and leave the house by the front door, the alarm sounds for 20 seconds and then turns off. But now, the alarm goes off indefinitely. Once I open the door to enter the house, the alarm goes off, and I can turn it off as usual. What is the problem? Where is the 12V battery?

Answer: The 12-volt battery should be in an alarm panel box where the wires from all the zones feed into, or in a combined keypad/alarm panel. If the exit tone goes off indefinitely, that means the contact on the door may be working intermittently and should be replaced.

Question: The external bell on my alarm is not working, but the internal one is. How do you fix the external bell?

Answer: It could be a fault with the wiring going to the bell if it's wired. However, it's more likely to be due to a fault in the bell (possibly caused by moisture ingress). If the bell is wireless and solar powered, there could be an issue with the battery/charging circuitry.

Question: Hi I have an SI compact alarm in the house and for no apparent reason the attack led is lit and nothing is responding on the keypad. Any ideas how to resolve this problem without having to call someone out?

Answer: Some large style panic buttons need to be manually returned to the un-pushed-in state with a key. Check whether you have one of these in the house and if so reset it. If you have any other type of panic device, it may need to be reset before resetting the panel.

I'm not sure whether this is the model of your alarm, but if it has inadvertently gone into alarm test mode (the attack led blinks when it is in this mode), pressing reset twice exits test mode and program mode.

Question: What is a tamper on an alarm system?

Answer: In a wired alarm system, a pair of cores in the cable connecting sensors to the control panel is used for tamper. If the cable is cut by a burglar to prepare for a subsequent break in, the panel will issue an audible or visual warning, even if the system isn't armed. Sensors, bell boxes, junction boxes, auxiliary sounders, keypads and other devices are normally provided with miniature tamper switch contacts that open when the devices have their lids or covers removed. The tamper pair of wires in the 6 core cable is also connected to tamper terminals in each device (these terminals connected to the tamper switches). If a device is opened, the tamper circuit opens and triggers a warning (or sets off the alarm, if it's armed).

Question: We have reed switches at the doors, what is the possibility of hot or cold temperatures to cause them to make a false alarm?

Answer: Possibly expansion and contraction of the tiny metal strips in the reeds as the temperature changes could cause false alarms. Another possibility is that the magnet and switch are too far apart. Usually, the gap shouldn't be more than 1cm or whatever the manufacturers recommend. If the gap is too great, the switch may be only barely held closed and any temperature changes or vibration could shake it open. The reed may also be faulty or low quality. I've had to replace lots of contacts, mostly on windows that were only rarely opened. So they seem to "stick" if not "exercised"

Question: My alarm went off and now shows that something is wrong in zone 3, the main level of my home. I opened all the windows and reclosed them, but can not get the alarm to come back on. Ay suggestions?

Answer: If it's a wireless alarm, it could be that the batteries are flat in one of the sensors. However, your panel should tell you this. Any recent renovations could also have upset the wiring.

If tampering occurred (possibly due to a nosy transient), you might have to reset the alarm.

Question: I have a hard-wired alarm system with a Napco RP1054e keypad. It has been working fine for over 18 years. The other day, the alarm keypad alarm was sounding, while showing a code 11 on the screen. I was able to get the alarm to stop but now the code is 8, and I can't activate the alarm. Any idea how I can fix this?

Answer: This is the manual for the pad.

Unfortunately there doesn't seem to be any info on status messages.

Question: When the alarm is activated (e.g., Overnight), a downstairs PIR sensor goes into alarm when I am walking in the room above, as if it is affected by vibrations. This just started a few days ago. Any thoughts as to why and where I should start looking at the issue?

Answer: It does sound as though there could be an issue with loose connections in the sensor, wiring, junction boxes, etc.

Is the sensor wired and definitely on its zone, and not looped in series with window contacts or shock sensors? Contacts can go open circuit if the magnet is mounted too far away or has gone weak or the reed switch is faulty, and there's vibration.

I would try covering the sensor with something to shield it so that it doesn't pick up body heat (e.g., a piece of card taped on). Then try tapping the case of the sensor to see if it triggers. The tamper switch on the PCB may not be held tightly closed with the cover in place. I had an issue like this with my system and tapping the PIR triggered an alarm. It turned out that the little piece of rubber on the front part of the sensor didn't push tightly down on the microswitch with the front replaced.

Question: What is causing my PIR sensors to malfunction?

Answer: A blown fuse could possibly be the cause of your problem (it could be marked "auxiliary"), or loose connections, cut or broken wires, shorted wires on a loop, upstream of the sensors (the panel side) or flat batteries on wireless systems.

Question: I have an ADEMCO Vista 10SE system. The monitor service has been terminated for several years. Recently I armed the system, but opening the door won't trigger the alarm. When I tested the door, I can hear a chime. The keypad shows a low battery. Could this be the reason why I can't set up the alarm?

Answer: Sensors can be temperamental and get stuck sometimes. Try tapping the door sensor if it doesn't trigger the alarm to see if this is the case.

This is the manual just in case you haven't got it.

Question: Our Veritas R8 alarm kept going off with the tamper light on. I replaced it with a new one. Now I cannot put it into Unset Mode. Each time I put my code in, the keypad only has the Unset light on. As soon as one of the sensors are activated, the alarm goes off even though it was under. I cannot get it to go into unset mode. What’s going on with it?

Answer: Sounds like there's a problem with tamper on a sensor or a tamper core in the cable if the alarm is wired. If you've replaced the panel, it eliminates a panel issue, so you'll just have to track down the fault in the wiring/sensor.

Question: I recently terminated my land line. Now my burglar alarm shows a problem with the phone lines. How do I bypass my burglar alarm?

Answer: If you can find a programming guide for your alarm, you may be able to disable monitoring for a phone line in the settings.

Question: I have an optima g4 alarm and have zone 1 set on a chime for entry-exit. Just recently the alarm will chime on zone 1 even when the door hasn’t opened. Also during the night for some reason when the alarm is armed, zone 1 will activate when the door hasn’t been opened beginning the countdown for the panel to go into alarm mode. Do you have any ideas?

Answer: I can't answer questions on specific models because there's just so many variations, however in general, this could be an issue with the sensor magnet becoming weak on the door, a faulty sensor on the door frame, loose connections in wiring, low batteries if the alarm is wireless and an aging backup battery in the control panel. Probably best to get a service technician to check out the system and possibly replace the sensor.

© 2014 Eugene Brennan


Eugene Brennan (author) from Ireland on July 24, 2020:

Thanks for getting back to me Mark!

Another satisfied customer!

(You can disable that delay if you want)

Mark-spencer on July 24, 2020:

Hi Eugene.

you were spot on! the external alarm kicks in after 30 seconds. thank you so much for you help!!!!

have a great day.

mark-spencer on July 21, 2020:

Hi Eugene,

thank you so much for the quick reply and the expert information!!!!! my friend is away for a few days but when he gets back i will get him to try out your idea..

thank you again!, i will let you know if it works as you expect.

Eugene Brennan (author) from Ireland on July 21, 2020:

Hi Mark,

This could be the issue.

Apparently the alarm has a second dual-ply timer that delays the external sounder activating for 30 seconds after the internal sounder activates if you don't enter the correct password after entering.. The idea of the internal sounder activating first is to scare away potential burglars trying to enter a code, and the delay is so that genuine people have an additional 30 seconds to get it right before the external sounder activates and disturbs the neighbours. This timer is enabled by default. The manual shows you how to disable it. So just try not putting in the code and see if the sounder activates after this period.

Eugene Brennan (author) from Ireland on July 21, 2020:

Hi Mark,

Usually one zone/contact is setup as an entry-exit zone which I presume the side door contact is because it doesn't trigger an alarm straight away unless you don't enter a code. There's probably an option in the settings in the engineer menu where you can specify whether the internal sounder (in the panel or a separate device indoors) or the external sounder or both activate for that zone.

Edit: Just found the manual:

I notice that zone 2 can be set for normal alarm or as an entry route. By "entry route", I think they mean what I call a walk through zone. So for instance if the side door contact is on zone 1 and is activated first by opening a door and the PIR is on zone 2 and it is triggered next (if it picks you up when you enter ), the alarm doesn't activate. But if if the PIR is activated first, it triggers an alarm straight away.

Another thing is that the part set alarm response can be set to full alarm or internal sounder. However there doesn't appear to be an option to apply this option to specific zones.

You might like to pose the question on thesecurityinstaller forum.

mark-spencer on July 21, 2020:

Hi, i have recently replaced a 9448+ control panel on a friends garage alarm, the alarm has just 2 sensors; One PIR and one door contact (on the side door).

If the PIR is triggered (ie someone has entered the garage by the up and over door) then both the control panel and the external bell will ring. however if i enter the side door and do not enter the code then only the control panel will alarm. is there a way to set the external bell to alarm in both cases? any advise appreciated :)

Bernard McNamee on April 21, 2020:

superb Eugene, thank you

Eugene Brennan (author) from Ireland on April 15, 2020:

That's great, thanks for the feedback!

KentGuy on April 15, 2020:

Hi Eugene

I am pleased to say that the alarm problem is now resolved . We changed and updated all the PIR’s for new ones and that has solved it. 3 days on all is well, so it must have been a faulty PIR, most of which were about 29 years old to be fair.

I bet the new ones don’t last as long as that !

Anyway, thanks once again for your help and advice...

Eugene Brennan (author) from Ireland on April 15, 2020:

Hi James. Possibly faulty sensors, loose connections or low batteries on wireless sensors. The panel may should give an indication of low battery power either as a notification or from within the menu. If the zones include contacts, magnets may be too far away from the contacts.

James Arthur Childs on April 15, 2020:

when I do a walk test 2 zones are permanently on. can you help?

thank you

KentGuy on April 11, 2020:

Many thanks Eugene.

This afternoon the fault appears to have corrected itself and all the PIR’s functioning as they should. The alarm can be set now and otherwise operates as it ought to. Albeit I do expect the fault to return.

The alarm panel itself has been replaced recently and is new. The intermittent fault was also there when the old panel was installed albeit it was 30 years old and needed updating.

Therefore I will check all that you have suggested next week. I will also replace all the PIR’s as they are very old and could do with updating. Hopefully that will resolve matters.. very many thanks for your very kind advice and assistance.

Eugene Brennan (author) from Ireland on April 11, 2020:

Unless the cable has been physically damaged by renovations or whatever, I'd be more likely to suspect bad connections. A short on the cable or overload from a bad sensor would pull the voltage down all the way to the panel. I doubt whether the 12 -4.5 = 7.5 volt drop is along the resistance of the cable itself, more likely this voltage is dropped at a connection somewhere. Check the voltage at the junction box before you remove the cables and examine the the connections there to see if they're ok. Don't forget also to check the return ground at the panel and junction box also. The drop could be on this line.

KentGuy on April 10, 2020:

Thanks Eugene for your very prompt reply. There seem to be four power feeds joined into a junction box between the power supply and the PIR’s.. the next step was going to be to remove one of these power cables at a time to see which PIR’s lose power and to see if the remaining PIR’s then activate and behave normally..If that works out then the plan would be to replace the PIR’s on the cable run that was adversely affected. If that solves the problem then the PIR/PIR’s on that cable run were causing the problem. If that does not work then the next step would be to suspect that the cable itself on that cable run is faulty. Would that make sense to you ? Many, many thanks Eugene for your valued advice...

Eugene Brennan (author) from Ireland on April 10, 2020:

A 12 volt PIR sensor will typically draw about 10ma, so that's around 100mA for 9 of them, which should be within the spec of the 12 volt supply on the panel. Usually this can supply 1 to 1.5 amps. One of the PIRs could be faulty and pulling down the voltage on the line, but another possibility is that there's a corroded connection somewhere along the line, causing a voltage drop. If the sensors are daisy chained together, then the supply voltage would be lower, all the way "down stream" of this bad connection. Are there any junction boxes between the first PIR and the panel where there could be a drop? Is there low voltage at this first PIR? Are there separate cables from the panel feeding each of the PIRs? Check also that there isn't any corrosion on the wire/wires screwed into the 12 volt supply terminals on the panel.

KentGuy on April 10, 2020:

Hi Eugene. Fault has found to be a Power drop on PIR circuit. Reads as12v at power supply but drops to 4.5v at PIR’s. System is wired with 9 PIR’s.

We think that one of the PIR’s may be faulty that is pulling down the power on the rest of the circuit. Would you concur ?

All zones are affected and each PIR flashes on and off weakly. Thanks for your kind attention Eugene

Eugene Brennan (author) from Ireland on April 02, 2020:

If you mean the issue started after you connected a PIR, all I can suggest is you disconnect it and maybe power down the panel and power it up again to see if it resets it.

Kyle on April 02, 2020:

Honeywell center. All wired, after conecting last PIR. Key now showing zone 3 red light. None of the keys work and cant get into programme engineers board. Can you help

Eugene Brennan (author) from Ireland on January 11, 2020:

You may have blown a fuse when you cut through the cable. Usually PIR sensors are powered by a 12 volt auxiliary supply. Fuses at the panel are normally 20mm glass types. Always replace with the same type ("F" fast or "T" time lag) and current rating.

Khan on January 10, 2020:

Hi. Ive cut my PIR wire to one sensor..ive managed to fixed 2 of tbe wires i and red but the alarm is stillnot working

Eugene Brennan (author) from Ireland on November 22, 2019:

That's odd. Possibly something has become damaged. Maybe the battery voltage was too low for an extended period and now won't charge fully. Or possibly the flashing indicates a power fault that must be acknowledged by an engineer. However this isn't usually the case.

Yorkie1952 on November 22, 2019:

Since power cut my alarm pad flashes whenever it is used when it did not do so before power cut. Have changed back up battery but that did not clear problem.

Colin on August 30, 2019:


Eugene Brennan (author) from Ireland on August 29, 2019:

Not sure. You can open the keypad, but it'll generate a fault tone or possibly set off an alarm even of it's not armed. Generally there are 4 wires feeding a wired keypad if it's separate, two of which will be power. If you power down the alarm by disconnecting any incoming power and battery, the external sounder will still operate if it has a backup bell. Maybe post a question on the alarm installers UK website who will know about specific alarm panels.

Colin on August 29, 2019:

I have a paragon and the key pad has stopped working , how do I disable the system so that I can check the key pad?

Eugene Brennan (author) from Ireland on June 21, 2019:

It certainly is possible. It's just a matter of tracing wires/voltages. You can do a continuity test between two ends of the core (using a long piece of waste wire onto the end of one of the probes of a multimeter). Make sure you disconnect one of the ends of the wire before doing a continuity test as any voltages present could affect readings or damage the meter.

Ged on June 21, 2019:

This pir was an add on to original system.

I kept getting pir fault so decided to change. Its after i changed it the power was lost. Now on the other side of the wall is the internal siren. Is it possible the engineer took a live feed to the pir from the siren and ive pulled it loose when i pulled the cable

Eugene Brennan (author) from Ireland on June 21, 2019:

There could be several reasons for the problem:

Break in positive supply to PIR.

Break in ground supply to PIR.

Have you had builders in who could have damaged cables?

If the zone is on a separate auxiliary power output in the panel to the working zone, this could output could have failed, or a fuse may have blown.

Check the connections on the panel to make sure the cores in the cable that carry power to the zone are tightened firmly and wires aren't corroded.

A fault in the PIR could be pulling down the supply also, but in general a single auxiliary supply powers all zones so you would lose power on the other zone also.

Ged on June 21, 2019:

I ve stopped getting power to one pir others are fine.

If i omit that zone it sets if not the alarm goes off

Murat Yapar on June 12, 2019:

Thank you so much, I appreciate it. I will follow these instructions one by one. If I come across another problem I will knock your door for more advices :). I am really grateful.

Best regards

Eugene Brennan (author) from Ireland on June 12, 2019:

Sounds like it could be a problem with the panel itself.

You could try disconnecting the zone and adding a wire link (or a 4.7 k resistor if the alarm is setup for EOL resistors). Then wait and see if you still get false alarms. Do the same if it's the tamper that's triggering the alarms.

Sensors can be triggered by hot /cold air currents moving over them from heaters or draughts. Birds, bats and other small animals can also cause false alarms. Possibly insects too. PIRs in my shed used to trigger and I have always wondered whether spiders walking over them could possibly have triggered the alarm.

Murat Yapar on June 11, 2019:


Thanks for all the valuable information above. I got a problem that could be solved I guess. I got 2 PIR sensors and 1 magnetic contact in my alarm system; my problem is two PIR sensors are causing false alarms; I got changed the wiring, module and sensors so far but after a while the problem starts again. It starts with a single sensor and time range of false alarms gets closer in time, whenever I start bypassing the faulty sensor, the problem jumps to the other one. What might be causing this? I would really appreciate if you could give me some clues.



Eugene Brennan (author) from Ireland on May 18, 2019:

Possibly a faulty sensor or low battery if the sensor is wireless although the panel should indicate this.

Anne Boyce on May 18, 2019:

Hi my alarm has developed a fault every time I walk past a sensor it makes a beeping sound like when it is setting and you are leaving the house, no faults are on the keypad,how can I fix this.

Garth Wight on March 29, 2019:

I need to remove the tamper switch. How do I hard wire the 4 contacts once the tamper switch is removed?

Eugene Brennan (author) from Ireland on March 26, 2019:

Check for any loose connections, moisture and tarnishing on the battery contacts (clean with wire wool). Check your battery with a battery tester, or better still replace. Usually these devices work on an inexpensive 12 volt battery (CR23A or similar).

Lindsey on March 26, 2019:

I opened up my garden PIR to change battery, and cleaned out an ant nest. Keypad still shows that circuit open. What else do I need to do? PIR is wireless - system is PowerSeries systemPK5508

Eugene Brennan (author) from Ireland on March 10, 2019:

It depends entirely on the model of the alarm. Most alarm manuals are available online, so if you can source that, it's probably just a matter of changing a setting.

Lou on March 09, 2019:

Every time you open the door it tells you what door is open how do I turn that off

David on February 27, 2019:

Hi i have alarm ks-858e how can i restat all

Craigside on February 25, 2019:

Hi Eugene

I will have a look for possible physical damage to the cable. Thanks again for your explanation!

Eugene Brennan (author) from Ireland on February 24, 2019:

Hi Rob,

Something along the line must be causing an increase in resistance. Since the new cable works fine, it obviously wasn't current load that was causing the drop, but resistance. Sometimes bad connections or corrosion can cause problems at the point where wires are wrapped under the heads of screws in a terminal, but you checked that. Maybe something sheared the cable under the ground? (Something heavy driving over it, building work, spades used during gardening) so that two ends of a broken core were just sitting in soil or even water in the conduit. You would still measure 12 volts with no load (a multimeter has an impedance of 10 mega ohm), but because of the gap and resistance, current flowing to a sensor would cause a drop.

Could mice have gotten into the conduit and bitten through the cable, or is it only narrow gauge conduit?

Craigside on February 24, 2019:

Hi Eugene

I've now traced and excavated a 6core cable and used of the 2 cores to supply 12V to the 40m point. My beams now all have a healthy 12V supply and its all working again.

I don't understand how my 1st run of cable, in conduits along with all the rest, laid and buried in 2005 has now developed a fault where it carries 12V ok, but then the voltage drops as soon as there is any tiny load on it. There has been no movement or activity where these conduits run, ie nothing to affect it?

I wonder what type of fault in a cable can manifest itself like this?

Many thanks, Rob

Craigside on February 24, 2019:


With all the devices (ie beams) disconnected on the 1mm cable, the voltage shows as 12V at the 1st point (40m). If I connect the cable (no devices just the cable run to the very end 100m) it shows 12V at each device location along the way.

If I then connect a device at the 40m point it drops to 6V. At my panel I disconnected from the 'Aux out' and connected to a 12V battery, same result 6V 40m away at the 1st device.

I tried a different device (brand new beam), still drops to 6V.

I now test on an existing 6core alarm cable along the same run to the 40m point, with new device connected it's showing 12V. I then connect this 6core back to panel Aux, at the 40m point it still showing 12V.

This seems to suggest to me that the 1mm cable maybe causing the issue?

Eugene Brennan (author) from Ireland on February 24, 2019:

That's 0.197 amps in total so even at 100m, voltage drop should only work out at 0.68 volts, based on that calculator. You could use other ones to confirm it's correct.

Craigside on February 24, 2019:

Yes, the thicker cable looks like just over 1mm diam.

On this cable, affected by this voltage loss problem I have the following sensors, the 1st of which is about 40m away;

3 x trans@ 27mA max, 2 x receivers @ 58mA max.

Eugene Brennan (author) from Ireland on February 23, 2019:

Edit. My calculation for 0.22 square mm cable was wrong. Voltage drop is 15.6 volts per 100m per amp.

Eugene Brennan (author) from Ireland on February 23, 2019:

By 1mm cable you mean 1 square mm CSA, diameter is 1.13 mm using the formula for area of a circle. Putting this into the calculator gives a drop of 3.43 volts per amp per 100m.

Eugene Brennan (author) from Ireland on February 23, 2019:

With no sensors connected, you should get 12 volts at the end of the cable, irrespective of it's length. If there's no current, there will be no voltage drop. As regards powering the units on a spare pair of cores, according to this datasheet....

... current capacity is 1A for 0.22 square mm. If cables are enclosed in insulation, the derating factor (for mains anyway) is 0.5, which means cables can only carry half that current. You could check the current requirement for your sensors from the spec, and see whether it falls within this rating. I would think the beams would need more power than the receivers, but the latter probably wouldn't need more than tens of mA. You could use your meter to measure the current.

I just checked this voltage drop calculator.

For 0.22 square mm CSA cable (I worked out the diameter from this), voltage drop is 17.5 volts per amp over 100m. So on second thoughts unless the sensors are using very little current, it mightn't be a good idea to use the alarm cores.

I didn't realise it was this high. It might explain why my alarm goes off so often in my workshop because of all the shock sensors and PIRs. All the small current demands add up to give something substantial.

Craigside on February 23, 2019:

... further to this...

I've also got 6 core alarm cable running alongside the 2core power cable (to the receiver units anyway). Would I expect a voltage drop on standard alarm cable over this distance? ie. I could use a spare pair on the 6 core to carry the 12V to these beams?

Your advice is much appreciated.

Craigside on February 23, 2019:

Hi, thanks for the speedy reply. Today, going against logic I fitted a new battery, and of course you are correct the battery isn't the problem!

Today I traced the cable (it's twin core 1mm to avoid voltage drop over the distance), it's in conduit buried, total approx 100m and carries the power from the panel to 3 sets of beams along the way.

At the panel it is reading 12V on my meter, the cable appears to be intact/undamaged and I've checked the connections. Having just read your post I've disconnected each sensor and taped the cable ends, and at the 1st junction (1st beam unit) it is now reading just 6V. There's no rust or poor connections I can see.

I'm thinking my next step would be to run a length of new cable overground to the 1st junction and see if that can show 12V at 50m from the panel?

Eugene Brennan (author) from Ireland on February 22, 2019:

...Regarding the answer below, another possibility is that one of the sensors is faulty, pulling excessive current. This may cause a voltage drop along the 100m of cable because it is light gauge. Voltage drop equals current x resistance of conductor.

Eugene Brennan (author) from Ireland on February 22, 2019:

The fact that the battery could be "tired" or aged shouldn't affect the auxiliary output voltage. A 12 volt regulator normally produces the auxiliary output and this is driven by a DC power supply powered by mains. If voltage is only 9 volts at the sensor, 3 volts is being dropped somewhere, possibly due to corroded screw terminals somewhere along the line. If the sensors were loading the auxiliary supply, voltage would also be low at the panel. Check the first sensor in the line closest to the panel and if voltage is low, a drop is occurring somewhere upstream between the sensor and panel.

I'm not 100% sure, but you should be able to power the sensors from a separate supply. When a sensor is triggered, a relay in the sensor operates and a pair of contacts opens. These contacts are normally volts free. This means that there is nothing connected to them, just wires to screw terminals that you can access. However you shouldn't need a separate power supply. For instance these beams only take 17mA, and the auxiliary power supply can normally source 0.5 to 1A,

Craigside on February 22, 2019:

I have a Veritas 8 panel alarm which includes 4 pairs of outdoor Aleph IR beams, furthest distance IR beam is located 100m from panel/PSU. System has worked great for 8 years. I'm now seeing false alarms from 2 of the IR beam pairs. On investigation, I discover that the voltage at the sensor is only 9V, and at the panel Aux is 12v. If the panel battery was 'tired', would this reduce the amps available to drive the detectors on the system, and therefore a lower voltage at the extremities of the system? Also, could I add a separate 12V PSU and connect it to the circuit (ie would it harm the Veritas 8 panel?). Many thanks!

Eugene Brennan (author) from Ireland on November 26, 2018:

It sounds like a faulty sensor. The magnet may have weakened over time or it could have been placed too far from the sensor originally. If your alarm system gives an audible indication of which zones are still open, you can try going to each sensor and holding a magnet against it to see whether the additional magnetic field closes it. Alternatively try tapping each sensor to see whether it closes. By a process of elimination, this may help you identify the faulty one.

Graham Els on November 25, 2018:

My alarm shows a fault when arming for a zone which uses a magnetic sensor. It will set as normal if I isolate the zone. Could this mean I have a faulty sensor or is there a bigger issue

Eugene Brennan (author) from Ireland on November 21, 2018:

If components have burned out, it's probably best to replace the whole unit because other components could have failed also and it wouldn't be worth the effort of troubleshooting. Also I found that the lacquer coating on the PCB of my bell had broken down over time due to the high voltages involved (several hundred volts) and moisture, causing tracks and components to fail due to arcing. Boards with LED strobes aren't prone to this problem, although the strobe isn't as bright as a xenon tube.

I doubt whether hitting the bell box would have done any damage unless the poles actually penetrated the box, or shook something loose from the PCB which shorted out components.

Oscar García on November 21, 2018:

This morning my Honeywell Accent G4 alarm went off but read no faults on the keypad, so I had to get out my ladders and disconnect the battery in the siren (is a RESON8 Bell Box, 8EP420). On closer inspection of the siren electronics I have a resistor burnt out, the Strobe tube has burnt out too.

This happened after the builders dismantle the scaffolding, it could be due to them hitting the bell box while moving the scaffolding?

Thank you very much in advance for your help.

Best regards,

Oscar García

Eugene Brennan (author) from Ireland on October 27, 2018:

I don't know Phil, I can't suggest solutions for specific models, just answer general questions. Try this forum:

Phil on October 26, 2018:

Put my Accenta 8 mini in engineer mode (prog 9999) removed cover on pir then replaced pressed set to restore instead reset now keypad has locked out.

Do I need to power down to restore the system.

barrie dovey on October 05, 2018:

just fitted a replacement pir is312 now the led"s will not light up

Eugene Brennan (author) from Ireland on August 28, 2018:

Hi Pete,

I'm not familiar with the panel but check page 69 of this guide where they mention black boxes on the LCD panel:

This might be of use also:

pete on August 28, 2018:

Hi, Eugene,

Our control panel just shows a series of black blocks, and does not respond to any entries made. It is a GARDTEC unit. There is some reference to an engineers code on the internet, I don't have that, but I know the password to set/unset the system.

Do you recognise this fault and know what this might be?

Many thanks


Eugene Brennan (author) from Ireland on August 25, 2018:

Have you tried to disarm it several times using the password? Possibly the keypad is giving trouble? It may be possible to reset the alarm by removing the cover and shorting out reset contacts. However the alarm will have to be reprogrammed with all settings again.

Joe on August 25, 2018:

My alarm is armed and I cant disarm it.

Eugene Brennan (author) from Ireland on August 11, 2018:

It could be the sensor, connections or even just transients on the line which are the most frustrating to troubleshoot because they are infrequent events, caused by a spike in voltage on adjacent mains cable or on the mains power supplying the alarm panel. You could try shorting the wires connected to the contacts in the sensor and see if it eliminates the problem which would indicate an issue with the sensor. If the sensor is the last in the line on a zone, it may have an EOL resistor as explained in the article.

gowestwardho on August 11, 2018:

I have a Ademco Vista-20P security system and lately when I am gone for a length of time I come home to find a "ALARM 08 LIVING ROOM MOTION" message. Clearly this indicates a failure of the one motion sensor but I do not know what to do about it? The system is 15 years old and this is the first issue I've had (other than replacing the battery twice). Has the motion sensor failed?, Is it a corroded or dirty connector? BTW, obviously based on its age this is a hardwired system. When I walk past the passive infrared motion sensor the red light comes on right away. And I removed the snap on cover and other than the mini circuit board I do not see a backup battery or anything. It is a large egg-shaped sensor and inside on a sticker it says "Aurora K3380V1 Listed Intrusion Detection Unit 885M". (But stamped into the inside of the plastic cover it also says "K3300V1 M6753"). Any advice?

Mike on August 04, 2018:

Please show a diagram between Texecom Varitas excel & SD1+ speech dialler

Eugene Brennan (author) from Ireland on June 28, 2018:

Try sending me a Facebook message. Follow the link on my profile.

Ricky on June 28, 2018:

Hi Eugene,

I have took a photo but I can't seem to send it to you via your profile as it won't let me add attachments. Please advise.



Eugene Brennan (author) from Ireland on June 28, 2018:

Can you take a photo and send it to me via my profile?

Ricky on June 28, 2018:

Hi again Eugene,

Thank you for your quick reply.

The model is an ITEC Meridian the sensors in question are as far as I know are the same company. Plain cover with barrel shape sensors.

I would be very grateful for you help.

Thank you.



Eugene Brennan (author) from Ireland on June 28, 2018:

Hi Ricky. Do you have any model information so I can look it up or maybe get an installation guide?

Ricky on June 28, 2018:

Hi Eugene,

Can you please tell me what the N - D markings mean on the end of the barrel shaped shock sensor please. If they are for orientation purposes then what direction should they face please.

Eugene Brennan (author) from Ireland on June 20, 2018:

Hi Harry. The only thing I can suggest is to remove any covers and check to make sure that no wires have come loose or have broken. If the sensors have a tamper switch kept closed by the cover, check this is being pushed down properly and the covers are seating ok.

Harry on June 20, 2018:

Hi i have just had doors changed and removed surface mounted door contacts fron & back, but now unable to set alarm, it states its is in Tamper mode i ahve reset using user code but still alarm will not set and the strobee goes off. the alarm is a Paragon E, could you advise how to over come this please

Eugene Brennan (author) from Ireland on June 15, 2018:

Hi Darrell,

The manual is available here:

You can view it online or download it as a PDF and read with Acrobat Reader which tends to be easier.

According to the info on page 12, the yellow ;ights indicates a problem, and the number of beeps plus the zone light illuminated tells you what it is.

On page 6, it seems to say you can acknowledge and ignore the problem and arm the alarm.

This is the programming manual. I'm not sure which option is for disabling monitoring of the phone line for disconnection or inability to report to a central station, possibly System Feature 26 - "Inhibit Failure to Communicate". (page As far as I can make out, you press # and the feature number, in this case #26 and then Key 3 to toggle this on. The problem is that if you start fiddling with the alarm and get it wrong. You might end up screwing it up and not being able to arm it. So it might be better to source a servicing company.

Darrell on June 14, 2018:

Hello Eugene

My security company went out of business and we never reestablished a service contract with another provider. It's been over a year now, and now my home alarm system has a yellow communication warning alarm. I can enter a code to turn the alarm off, but I always have a yellow warning L.E.D. light on my front keypad. I'm assuming the system thinks someone has cut my pone line so it generates the code. Question? Does an alarm system have to be re-programed with phone service disabled in order for me to continue to use my system for all the sensors, even if I don't use a service provider?

NAPCO XP-600 Alarm

Eugene Brennan (author) from Ireland on June 12, 2018:

You may be able to acknowledge the event and prevent further notifications. Exiting/entering the house isn't an alarm condition though unless the entry/exit time is exceed and the alarm is triggered. So you need to edit the setup to eliminate the notifications or get your alarm company to do so.

Alison Smith on June 12, 2018:

my alarm has started to ring our mobiles to notify us when we exit or enter the house. How do we stop this? Very annoying


Eugene Brennan (author) from Ireland on May 03, 2018:

Hi Tyrone,

Yes it is.

Just loop the contacts of the magnetic contact sensors and PIRs in series.

Use an EOL resistor at the end of the loop if the panel requires it and resistors across each sensor if the alarm is a FSL system.

Tyrone on May 03, 2018:

Hi, is it possible to connect contact sensors and a PIR using the same cable for the same zone?

Eugene Brennan (author) from Ireland on April 24, 2018:

Hi Dave, on some alarms, entering the alarm code turns off the alarm plus you may have to press a further key/keys to reset it. Do you have a user manual for the alarm?

Dave on April 24, 2018:

HI, I tried to open the cover on the alarm panel of my honeywell alarm and the alarm sounded. I turned it off by entering my code but now I'm locked out of the system with the spanner light flashing? there's obviously a sensor inside, how do i reset it?

Eugene Brennan (author) from Ireland on April 05, 2018:

It could be, but check that any fuses are ok. These are often 20mm, 1A glass types. Replace fuses only with the same type.

Walshe2 on April 05, 2018:

Hi,I have a hkc outside bell box that is not going off in an alarm situation so I replaced it with a new one and have the same problem.I have checked all cables but found that back at the control panel there is no voltage at the external bell terminals.could the PCB be faulty???

Eugene Brennan (author) from Ireland on March 20, 2018:

Hi Damion,

Voltage is usually 12 volts to sensors/contacts, so not a hazard, but to be doubly sure there isn't a mains electrical wire putting dangerous voltages on the wiring, you can always check with a neon phase tester screwdriver.

The issue could be due to a loose wire. It can also be caused by a faulty contact, but sometimes the magnet can lose strength and not keep the contact closed anymore, especially if the magnet wasn't mounted close enough to the contact in the first place. Contact/magnet spacing should be 1 cm at the most. You could try moving the magnet closer (maybe put some sort of spacer underneath) and see if it improves matters.

Damion on March 20, 2018:

Hi, There appears to be an issue with the front door magnetic sensor. The door is closed but we are hearing a "beep" as though the door has opened. This then sets off the house alarm. I tried to move the wire by the sensor the beep occurs. Could this just be a loose wire? is there much voltage within the sensors so that I know its safe to check myself?

Eugene Brennan (author) from Ireland on March 11, 2018:

Haven't been able to find any info on the Abacus panel, but try and they might be able to help.

Eugene Brennan (author) from Ireland on March 08, 2018:

Hi Chris,

I'll see if I can find any reference to the error and get back to you tomorrow.

Chris J on March 08, 2018:

Hi Eugene

I have an Abacus LCD alarm panel and all of a sudden its started playing up a little. Its fine until the alarm is set and then as soon as its armed it will sound after around a minute every time, the log shows the reason for the alarm to trigger as "KP1 Engnr". Any clues what could be causing it?

I've already tested the battery in the main box and the voltage is constant and fine.

Any helps appreciated, very nice of you to help all these people through your site.


Eugene Brennan (author) from Ireland on March 04, 2018:

Hi Rami,

The Veritas R8 is not wireless unless a module has been added to make it so. A sensor that acts up could be faulty, require a battery if it's wireless, or the wiring has developed a fault somewhere along the line, perhaps due to renovations. Motion sensors can also be triggered by sudden changes in temperature e.g. if they face a window or radiator.

Rami T on March 04, 2018:

Hi Eugene

I have Veritas R8 from Texecom . I think it is wireless. one of the motion detectors kept alarming unnecessarily on/off!

What do you think the problem is?

Thanks for answering

Eugene Brennan (author) from Ireland on February 28, 2018:

Is this a wireless system? The battery may need replacement in the keypad.

If the system is wired, and this is a remote auxiliary keypad, again there could be a flat battery in the pad.

If the keypad is wired and separate to the main alarm panel, connection box, trace the wiring and see if the panel/box is feeding the keypad with 12 volts. There may be a fuse blown in the panel, so check that first.

david on February 28, 2018:

my key pad has no power to it yet my sensors are lighting up red help

Eugene Brennan (author) from Ireland on February 19, 2018:

Hi Lindsay,

Normally external sirens won't activate unless the system is armed and you start opening sensors, the panel, junction boxes etc. However if you do the same when the system is unarmed, a sounder will normally activate on the panel to indicate that tamper loops have gone open circuit. Whenever I'm working on my panel and this happens, I just enter the code to silence the sounder. The external siren will operate if the wiring for a panic switch goes o/c, or the cover is opened, irrespective of whether the system is armed or not, so you may want to have a wire link ready to short out the contacts until you're ready to replace the cover on the switch if it's a wired type. I'm not sure about engineer mode on your panel. Usually there's a time period during which work can be done before any sounders operate, but even if that happens, I'm sure you can just exit and re-enter engineer's mode to reset this period.

Lindsay on February 19, 2018:

Hi, I need to change my magnetic door contactor, a vibration sensor and panic alarm switch. Thanks to internet info, I have managed to sus the engineers code for our Paragon Plus alarm; hence, once the system is in Engineers Mode, can I do the work without triggering the sirens?

Eugene Brennan (author) from Ireland on January 19, 2018:

Hi Jayne, If you knew the model of the alarm, it may be possible to source a manual to see what the flashing LED means.

You could try posting on this forum. There are lots of members who are installers and would be familiar with specific models of alarms.

Jayne on January 19, 2018:

Hi my telstar alarm green light on the control panel and the main box is flashing and id like to fix it how do i go about doing that? The company is out of business so i have no one to ring.

It dose work but it didnt do this before any idea? Thanks

Eugene Brennan (author) from Ireland on December 23, 2017:

Hi Maria,

There's probably an issue with the battery being charged. Possibly a blown fuse, or a fault in the charging electronics.

Check also mains power is going to the alarm. There may be an LED to indicate this on the panel (which may be a separate unit, or integrated with the keypad).