FAULT FINDING GUIDE

Security Alarm Electrical Fault: Alarm Wiring Problems Explained

Your security alarm is beeping, showing a fault indicator, or sounding unexpectedly. This guide explains tamper alerts, low battery faults, power supply problems, and communication failures — and tells you when to reset yourself versus when to call an engineer.

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11 min readUpdated 2026-05-18Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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Key Takeaways

  • 1Intruder alarm panels display fault conditions as a combination of LED indicators, displayed text, and audible tones. Understanding what each fault type means — tamper, low battery, power supply, line fault, or zone fault — is essential before attempting any reset or repair.
  • 2Tamper alerts are a deliberate security feature. They are triggered when a detector cover is removed, a cable is cut, or the panel enclosure is opened without authorisation. Tamper alerts should never be disabled — investigate the cause and rectify it.
  • 3Standby battery failure is the most common cause of security alarm faults in older installations. Most alarm panels specify a 12 V sealed lead-acid battery with a nominal 12 Ah capacity; a battery that fails to hold charge below 11.5 V under load must be replaced.
  • 4A security alarm that is sounding in fault mode (intermittent bell or sounder activations at irregular intervals, often at night) is almost always suffering from a low battery, mains power loss, or communication system fault rather than a genuine intruder detection.
  • 5Any work on the mains power supply section of a security alarm system must be carried out by a qualified electrician. The alarm panel transformer or switched-mode power supply unit is connected to the mains and must be treated as live electrical equipment.
01 · Fault Finding Guide

Tamper Alerts

The tamper circuit is one of the most important security features of a compliant intruder alarm installation. Every detection device, cable run, and the panel enclosure itself is monitored by a normally-closed tamper loop. Any break in this loop — whether caused by a detector cover being removed, a cable being cut, or an attempted intrusion into the panel — generates an immediate tamper alert.

  • Detector lid tamper — the most common tamper alert. A PIR or magnetic contact detector has had its cover removed, either accidentally (loose screw, impact) or deliberately. Identify the triggering device from the panel display, inspect it, and re-fit the cover securely. If the cover is missing or damaged, the detector must be replaced.
  • Cable tamper / anti-cut — some installations include anti-cut monitoring on the zone wiring. A cable that has been cut, pinched, or developed an open circuit will trigger this tamper. Cable tampers in accessible locations (loft voids, cupboards) are a known vulnerability — investigate and repair the cable run.
  • Panel enclosure tamper — the panel cabinet has a tamper switch that triggers if the lid is removed. If this alert is showing without a legitimate reason for the panel to have been opened, treat this as a potential security incident — check that the panel has not been interfered with.
  • Never disable the tamper circuit — defeat of the tamper circuit on an alarm system is a security vulnerability. If the tamper alert cannot be cleared after investigation, call an alarm engineer — do not programme out the tamper function.
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02 · Fault Finding Guide

Low Battery Faults

Standby battery failure is the most frequently encountered security alarm fault. The standby battery maintains system operation during mains power loss — it is a critical life-safety component for monitored systems and a compliance requirement for most commercial alarm installations.

  • Low battery threshold — most alarm panels generate a low battery warning when the standby battery voltage drops below approximately 11.5 V under load. This is typically 6 to 12 months before the battery fails completely, giving time for planned replacement.
  • Night-time sounder activation — a low standby battery causes the alarm to sound intermittently, often in the early hours of the morning when ambient temperature is lowest (cold reduces battery voltage). This is a common and extremely disruptive fault. Replace the battery to resolve it.
  • Wireless detector batteries — in wireless alarm systems, each detector has its own battery, typically a lithium primary cell rated for 3 to 5 years. Battery alerts from wireless detectors are shown on the panel display by zone or device. Replace wireless detector batteries in pairs (where applicable) and record the date.
  • Charging circuit fault — if a replacement battery also rapidly discharges, the fault is in the panel's battery charging circuit rather than the battery itself. The charging circuit is part of the panel electronics and requires engineer investigation.
03 · Fault Finding Guide

Power Supply Faults

The mains power supply section of a security alarm panel converts 230 V AC to the low-voltage DC required by the panel electronics, detectors, and sounder circuits. A mains power fault will cause the system to run from the standby battery — a temporary measure that becomes a fault condition if the mains is not restored within a reasonable time.

  • Mains power loss indication — most panels display a mains power fault (often a yellow or amber LED labelled AC or MAINS) when the 230 V supply to the panel is interrupted. The system continues to operate from the standby battery. Check for a tripped fused spur or MCB before assuming a panel fault.
  • Blown transformer fuse — the alarm panel transformer or SMPS may have an internal thermal fuse or a replaceable fuse on the panel PCB. A blown fuse is usually caused by a voltage transient, a fault in the bell or detector circuit, or an ageing transformer. This requires engineer attention — working inside an alarm panel on the mains section requires electrical competence.
  • Failed transformer or SMPS — an alarm panel power supply that fails to charge the battery or provide operating voltage, confirmed by measuring the DC output, indicates a failed transformer or SMPS unit. Replacement requires the correct approved part for the panel model.

A general electrician can check and rectify the mains supply circuit to the alarm panel (the fused spur, the MCB, and the 230 V supply cable). Work inside the panel enclosure should be left to an alarm engineer.

04 · Fault Finding Guide

Communication Faults on Monitored Systems

Monitored alarm systems send alerts to an alarm receiving centre (ARC) via telephone line, broadband, or GSM/4G cellular link. A communication fault means the ARC cannot receive alerts — the alarm will still sound locally, but police or key holder response will not be triggered.

  • PSTN line fault — traditional telephone line monitoring is being superseded by IP and cellular communication as the PSTN is phased out across the UK (scheduled completion 2027). Systems relying solely on PSTN should be upgraded to IP or cellular communication before the line is withdrawn.
  • IP / broadband communication fault — broadband outages, router failures, or changes to router settings (firewall rules, IP address changes) can break IP signalling. Most IP alarm communicators require a static IP or a router that supports port forwarding to the alarm panel. Check broadband connectivity and router settings.
  • GSM / 4G cellular fault — cellular communicators rely on mobile network coverage. A SIM that has expired, been deactivated, or is out of credit will cause a communication fault. Check the SIM status with the alarm company and verify mobile network coverage at the panel location.

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05 · Fault Finding Guide

When to Reset Yourself vs When to Call an Engineer

Knowing when it is appropriate to reset an alarm fault yourself, and when to call a qualified alarm engineer, can save time and cost while keeping the system secure.

  • Safe to reset yourself — a low battery alert where you have already replaced the battery (acknowledging the fault clears the alert), a tamper alert caused by a detector cover you have re-fitted securely, a mains power loss alert following a known power cut that has now been restored, or a false alarm from a zone that you have identified and addressed (clean a dirty detector lens, re-fit a loose magnetic contact).
  • Call an alarm engineer — any fault code you cannot identify from the manual, a tamper alert with no obvious physical cause, the alarm sounding during the set period without a zone trigger, a zone that repeatedly triggers false alarms, or any work that requires opening the panel enclosure and accessing the PCB or mains wiring.
  • Call an electrician (not the alarm company) — for a blown fuse or tripped MCB on the dedicated mains supply circuit to the alarm panel, damaged mains supply cable, or to advise on surge protection for the supply circuit.
06 · Fault Finding Guide

For Electricians: Security Alarm Electrical Work

Electricians are frequently asked to attend security alarm faults — particularly when the fault presents as a mains supply problem. Understanding the boundary between electrical installation work and alarm systems engineering helps set clear expectations with clients.

EICR and Security Alarm Systems

When carrying out an EICR on a property with a security alarm, inspect and test the dedicated mains supply circuit (typically a fused spur or small MCB). Note the presence of the alarm system in the schedule of particulars. Use the Elec-Mate EICR app to record observations and generate the report on site.

Minor Works on Alarm Supply Circuits

Replacing a fused spur, adding surge protection, or rectifying a supply cable fault on an alarm circuit requires a Minor Works Certificate. Use the Elec-Mate Minor Works app to generate compliant documentation on site.

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Frequently Asked Questions About Security Alarm Faults

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