Burglar Alarm False Alarms — Causes and How to Fix Them

False alarms are the most common complaint from alarm system owners — and one of the most preventable. Understanding the causes allows you to fix them quickly and protect your police-response eligibility.

Important: The Metropolitan Police operates a Confirmed Alarm Policy. Three or more unconfirmed false activations within 12 months results in removal of police response from your address. If your alarm has already false-alarmed more than once, address the cause urgently.

Pets triggering PIR sensors

Fix: Replace standard PIRs with pet-immune sensors rated to 25kg or 38kg. Dual-tech PIRs (PIR + microwave) further reduce false triggers from animals.

Spiders and insects on detector lenses

Fix: Clean detector lenses with a dry cloth quarterly. PIRs detect movement by sensing heat differential — a spider crossing the lens is enough to trigger the alarm.

Draughts moving lightweight curtains near PIRs

Fix: Reposition PIRs so they do not directly face curtains, blinds or plants that move in the breeze. Alternatively, reduce the detection angle using a PIR anti-masking lens.

Low or flat batteries in wireless devices

Fix: Replace batteries promptly when the panel displays a low-battery warning. Most wireless alarm systems give 30–60 days' notice before battery failure.

User error — forgetting to disarm

Fix: Increase the entry delay (typically 30–45 seconds is sufficient for most properties). Add a keypad near the most-used entry point. Consider smart alarm app control to disarm remotely if you forget on the way out.

Faults in door or window contacts

Fix: Door contacts that are misaligned or have corroded contacts will trigger a tamper or zone alarm. Realign or replace faulty contacts — an annual service catches these before they cause nuisance alarms.

Heat sources near PIRs

Fix: Boilers, radiators, air vents, sunlight through glass and open fires can all fool a standard PIR. Reposition sensors away from heat sources or upgrade to dual-tech detectors.

Subsidence or building movement

Fix: In older properties, vibration detectors or shock sensors on windows can trigger if the building moves in high winds. Adjust sensitivity or switch to a different detector type.

When to call an engineer

If your alarm has false-alarmed more than twice in the last six months and you cannot identify the cause, call your installing company to carry out a full system inspection. If your alarm is out of warranty or was installed by a company that is no longer trading, Sure Alarms provides takeover surveys — we will assess the system and either service it or recommend a replacement where appropriate.

False Alarm? We Can Help

Sure Alarms carries out system inspections and false-alarm investigations across London and the Home Counties. Call 0800 130 3418 or request a callback below.