Why Does My Burglar Alarm Keep Going Off For No Reason?
Common causes of unexplained alarm activations and what you can check yourself
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A burglar alarm that triggers with nobody there is one of the most frustrating faults a homeowner can face, especially when it happens repeatedly or in the middle of the night. While it can feel random, there is almost always a specific trigger, even if it takes a bit of detective work to find it.
False activations are commonly linked to a single sensor picking up movement or vibration that is not an intruder, such as an insect near a PIR, a loose door contact, or curtains moving in a draught. Environmental factors like sudden temperature changes near a heater or window can also confuse motion detectors.
Checking the event log on your keypad or app is the fastest way to narrow down which zone triggered the alarm each time it happens. Once you know which sensor is involved, it is often possible to identify a pattern, such as a particular time of day or weather condition, that points to the cause.
What You Will Usually Notice
Safe Checks You Can Do Yourself
Check the event log for the triggered zone
Use the keypad menu or linked app to see exactly which sensor caused the activation and at what time. This is the single most useful piece of information for narrowing down the cause.
Look at the sensor's surroundings
Check whether curtains, balloons, hanging decorations or a pet's usual route could be passing in front of a PIR. Moving these items away from the detector's field of view often solves the problem immediately.
Confirm doors and windows are properly latched
A door that is not fully closed can move slightly in the wind and repeatedly trigger a contact sensor. Check each protected opening closes firmly and the contact aligns correctly.
Check for insects or dust on visible detector covers
Wipe the outside cover of any PIR you can safely reach with a dry cloth, as cobwebs or insects on the lens can sometimes cause false readings on sensitive detectors.
Review recent changes around the property
Think about anything new near a sensor, such as a houseplant, a new pet, or furniture moved into the detection zone, as these are common and easily overlooked causes of false triggers.
What Normally Causes It
Insects or spiders inside a PIR detector
A small insect crawling across the internal lens of a motion sensor can trigger a false activation, particularly in warmer months when insects are more active around the home.
Draughts moving curtains or blinds
PIR sensors detect movement and heat, so curtains or blinds swaying in a draught near a window can occasionally be picked up as motion, especially if the detector is close by.
A pet moving within a sensor's range
Even sensors marketed as pet friendly have size and weight limits, so cats or larger dogs moving through a room can sometimes trigger a PIR that was not set up with them in mind.
A loose or misaligned door or window contact
If a contact sensor has come slightly out of alignment, normal movement of the door in the wind can register as an opening and closing event, triggering the alarm unexpectedly.
Sudden temperature changes near a detector
Heaters, sunlight through a window, or cold draughts can cause rapid temperature shifts that some motion detectors interpret as movement, particularly older or poorly sited sensors.
A fault developing within a sensor itself
Over time, internal components in a detector can degrade, causing it to become oversensitive or unreliable, which is more likely if the same zone triggers repeatedly with no obvious external cause.
When to Stop and Call an Engineer
Keeping it from coming back
Keep the area around PIR detectors clear of moving objects, pets and draughts, and check the event log periodically so a developing pattern of false triggers is caught early rather than becoming a regular disturbance.
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Frequently Asked Questions
Why Does My Burglar Alarm Keep Going Off For No Reason?: common questions
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