Why Does My Intruder Alarm Keep Going Off? Common Causes & Fixes
False alarms are frustrating and can lead to fines if police are repeatedly called out. Here are the most common causes and how to fix them.
A false alarm on an intruder alarm is more than an inconvenience. In the UK, the police operate a policy of withdrawn response — if your alarm generates too many false call-outs, they'll stop responding to it. This could leave your property unprotected in a genuine break-in.
If your alarm is triggering when it shouldn't, here are the most likely causes — and what to do about each one.
Common Causes of False Alarms
Low or flat backup battery
The most common cause. Most alarm panels have a backup battery that lasts 3–5 years. When it starts failing, the panel raises a tamper or fault alarm — often in the early hours when mains voltage dips slightly. Solution: have the battery replaced by an engineer.
Faulty or dirty detectors
PIR (passive infrared) detectors can trigger due to insects, spiders webs, dust build-up or direct sunlight. A spider walking across a lens at 3am is a surprisingly common cause of false alarms. Solution: regular servicing includes cleaning and testing all detectors.
Poorly positioned detectors
A PIR detector aimed at a window where morning sun creates rapid temperature changes, or one positioned above a radiator, will generate false triggers. Solution: detector repositioning or replacement with a dual-technology (dual-tech) detector.
Tamper faults on panels or detectors
If a detector cover is loose or the panel door hasn't been properly closed, a tamper alarm will trigger. Solution: check all covers are fully seated and the panel door is secure.
Communication faults
If your alarm is monitored via Redcare or IP, a fault in the phone line or broadband can cause the panel to raise a communication alarm. Solution: check your broadband and phone line, or ask your engineer to check the communicator.
User error
Insufficient exit/entry time, forgotten codes, or staff not knowing how to arm/disarm correctly. Solution: user retraining — your engineer can walk staff through the system at any service visit.
What to Do If Your Alarm Won't Stop Triggering
First, try to identify which zone is triggering — your panel keypad should display a zone number or name. Check that zone for obvious issues (loose detector, direct sunlight, spider web). If you can't identify the cause, isolate that zone on the panel if your system allows it, and call an engineer.
Do not leave the system isolated indefinitely — a zone-isolated alarm offers significantly reduced protection.
Prevention: Regular Servicing Reduces False Alarms
The majority of false alarms are preventable with annual servicing. A service visit includes cleaning all detectors, testing battery health, checking all connections for corrosion and reviewing the event log for developing faults before they become problems.
Intruder Alarm Fault? We Can Help.
Fortech Group provides intruder alarm repairs and servicing across London. We support all makes and models — including systems we didn't install.