Intruder Alarm Installation UK: Burglar Alarm Wiring Guide

• Wired systems — preferred for commercial — all detectors, keypads, and sirens are connected to the control panel by dedicated cable. No battery management, no RF interference risk, and lower ongoing maintenance cost. Tamper detection on cables is straightforward. Preferred for new builds, large commercial sites, and any installation where cable runs can be hidden. Install time is longer due to cabling.
• Wireless systems — suited to retrofits — detectors communicate with the panel via encrypted radio frequency (RF). No cable runs required, making installation in occupied buildings much faster and less disruptive. Requires battery management (typically 2–5 year battery life per device). Grade 2 wireless systems use frequency-hopping or encrypted protocols to resist jamming. Confirm RF signal strength at every device location before commissioning.
• Hybrid systems — combine wired zones on the main panel with wireless expansion zones for areas where cabling is impractical. Common on larger commercial sites or where phased installation is planned. The wired zones typically cover the most critical areas (perimeter, server rooms) and wireless covers secondary zones.

• Mounting height — standard PIRs should be mounted at 2.0–2.4 metres above floor level in corners, angled to provide coverage across the room. Too low and the detector may be defeated by crawling; too high and sensitivity decreases. Wide-angle PIRs (360°) can be ceiling-mounted — follow manufacturer guidance for optimum height.
• Avoid heat sources and draughts — do not mount PIRs where they face south-facing windows (direct sunlight), above radiators or fan heaters, near air conditioning vents, or adjacent to boilers. Temperature changes in the PIR's field of view trigger false alarms. A 50mm thermal buffer between the detector and any heat source is good practice.
• Pet-immune detectors — where pets are present, use pet-immune PIRs (also called pet-tolerant). These use a downward-looking lens pattern or dual-zone detection logic to ignore animals below a threshold weight (typically 15–25 kg). Confirm the pet's weight against the detector specification and test with the pet present.
• Walk-test every detector — after installation, walk-test every PIR to confirm coverage. Enter the detection zone from each direction the manufacturer specifies. Use the detector's walk-test LED to confirm activation. Document the walk-test results in the commissioning record.

• Surface-mounted vs flush-mounted — surface-mounted contacts are faster to install and visible (deterrent value). Flush-mounted contacts are hidden within the door frame and harder to defeat. High-security applications should use flush-mounted contacts with a guard magnet (anti-tamper magnet) to prevent defeat by an external magnet.
• Wiring convention — contacts are wired in a normally-closed (NC) loop. An open circuit (contact separated) triggers the alarm. This convention means a cut cable also triggers the alarm — an important anti-defeat measure. Each external door and accessible window should have its own dedicated zone.
• Double-pole contacts for metal frames — on metal door or window frames, use non-magnetic contact sets designed for metallic frames. Standard magnetic contacts do not work reliably on steel frames due to the magnetic shielding effect of the frame material.
• Shutter contacts and roller shutter detectors — for commercial premises with roller shutters, use dedicated shutter contacts or vibration detectors. Shutter contacts sense the position of the shutter; vibration detectors sense forced attack on a closed shutter. Dual-technology (contact + vibration) gives the most reliable coverage.

• Zone capacity — each detector or contact uses one zone (input). Count the total number of detectors, contacts, panic buttons, and auxiliary inputs required, then add 25 per cent headroom. A typical office with 20 detectors and 12 door contacts (32 zones) should be fitted with a 40-zone or greater panel.
• User codes and access levels — panels should support multiple user codes at different access levels: engineer code (full access), manager code (set/unset, zone bypass), user codes (set/unset only). Commercial sites need panels supporting 50+ user codes with individual audit trails.
• Partitioning — for multi-tenant or multi-use buildings, choose a panel that supports partitioned zones (areas). Each partition can be armed and disarmed independently. Essential for offices where different areas have different access times — for example, a warehouse that is locked at 6pm while the office remains occupied until 9pm.
• Communications module — for ARC monitoring, the panel requires a communicator: IP (broadband), GSM/4G, or dual-path (both). Grade 3 systems require dual-path communication. Ensure the selected communicator is compatible with your ARC's receiving equipment and protocols (SIA DC-09, Contact ID).

• Keyholder response — when an alarm is triggered, the ARC calls the keyholder list in sequence until someone confirms they are responding or requests a police response. This is the most common monitoring arrangement for domestic and small commercial systems. Annual monitoring cost: £150–£400.
• Police Unique Reference Number (URN) — for police response, the system must hold a URN issued by the local police service. URN conditions include NSI or SSAIB-approved installation, Grade 2 minimum, and a limit on false alarm activations per year (typically three false alarms result in URN withdrawal). Police response is not guaranteed and is subject to availability.
• Keyholding and mobile response — some ARCs offer a keyholding service where the ARC holds a set of keys and can dispatch a mobile security officer to attend the premises. Useful for sites where keyholders are not local or are frequently unavailable. Additional annual cost: £300–£800.
• Video-verified alarms — higher-tier ARCs offer video verification, where the ARC operator reviews CCTV footage when an alarm is triggered to confirm whether an intrusion is in progress before requesting police response. Significantly reduces false alarm calls and improves police response priority.

• NSI Gold — the highest level of NSI certification, required for Grade 3 and Grade 4 installations, for police-URN-eligible systems, and for most large commercial contracts. NSI Gold companies are assessed against PD 6662 (UK national guide to BS EN 50131) and are subject to unannounced audits.
• NSI Silver / SSAIB-approved — suitable for Grade 1 and Grade 2 domestic and light commercial systems. Still requires compliance with BS EN 50131 and ongoing auditing. Recognised by police services for URN issuance at domestic level.
• Insurance implications — most commercial insurers require NSI or SSAIB-approved installation to apply alarm-related premium discounts. Without approved installation, the insurer may refuse claims where an alarm was fitted but not to the required standard. Always check the insurer's specific requirements before specifying the system.

• Police URN — professional only — a Police URN for police response can only be issued for systems installed by NSI or SSAIB-approved companies. A self-installed system, however well-designed, cannot obtain a URN.
• Insurance requirements — domestic insurers vary. Some accept self-installed systems for modest premium discounts; most commercial insurers require professional installation. Read the policy wording carefully.
• DIY limitations — consumer-grade wireless systems (Ring, Ajax, DSC) are suitable for basic domestic applications and offer reasonable Grade 1 equivalent performance. They do not meet Grade 2 or Grade 3 requirements. False alarm rates on self-installed systems tend to be higher due to suboptimal detector placement.

Scope Demarcation: Know Your Interface

The electrician's scope typically covers cabling, cable containment, PSU wiring, and provision of a mains power supply to the panel location. Detection device placement, control panel commissioning, zone programming, and ARC/URN registration remain with the NSI/SSAIB-approved security company. Agree and document the interface in writing before mobilisation — the most common project failure is neither party completing the handover between electrical supply and panel commissioning (PWI: 'not recording excluded systems clearly', 'failing to define interfaces with other trades').