Window alarm false alarm: sun, gap, and noise
Updated: 16 October 2026
The siren is going off and nobody is at the glass, or you have knocked the pane and nothing happens. A window alarm false alarm here is usually sun or weather on a puck, a magnetic gap that still reads as open, or a unit that will not trip at all. By the end you should know which of those you have, and when the noise is a council matter. The rows are on the [window alarm comparison](/hub/burglar-protection/window-alarm). This page is from the Products Compared editorial team, using amazon.co.uk reviews plus GOV.UK and police sources, not a lab recreation. A qualifying purchase can earn a commission at no extra cost to you.
The siren is going off and nobody is at the glass, or you have knocked the pane and nothing happens.
The siren is going off and nobody is at the glass, or you have knocked the pane and nothing happens. A window alarm false alarm here is usually sun or weather on a puck, a magnetic gap that still reads as open, or a unit that will not trip at all. By the end you should know which of those you have, and when the noise is a council matter. The rows are on the window alarm comparison. This page is from the Products Compared editorial team, using amazon.co.uk reviews plus GOV.UK and police sources, not a lab recreation. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Sensor | Trigger | Modes | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  TECKNET TECKNET window and door alarm, 3-pack | Magnetic contact | Parts more than 2 cm apart | Off, chime, alarm; 3 volumes | 8.6 | about £13.99 | View offer |
| Preis-Tipp |  VOXON VOXON magnetic window alarm, 4-pack | Magnetic contact | More than 20 mm apart | Off, chime, alarm; no volume slider | 8.6 | about £12.74 | View offer |
| Alternative |  Defender Defender ultra-slim window alarm, 2-pack | Vibration | Shock or glass impact | On/off | 6.4 | about £14.95 | View offer |
On this page
Why a window alarm false alarm happens
Sort the symptom before you replace anything. A puck reacts to shock and, in the reviews, to sun. A contact reacts to the distance between two halves. Advice for a passive infrared sensor will not calm a puck or close a magnetic gap.
The National Protective Security Authority says vibration detectors may false-alarm in rain or hail. This set has no room listener, and no listing prints an IP rating. You can check the switch, the cells, the gap and the pane. You cannot turn a dial these listings do not include. Fitting from scratch is how to fit a window alarm.
Vibration puck: sun, rain, and no dial
Defender reviews describe trips on east-facing and south-facing glass, and units that will not trip. This page does not confirm heat expansion. The listing is on and off, with six LR44 cells and no sensitivity control. One knock after a fresh arm shows whether it is too keen or dead.
WER’s bullets say rain and wind should not trip it. One UK review says heavy rain did. Do not copy that denial onto Defender or Flintronic. Flintronic runs for 30 seconds and can start again. That is not a sensitivity setting. If the puck is too keen, switch it off or move it off the sun.
Magnetic contact: gap and a curved frame
A contact that sounds while you believe the window is shut is reading the halves as apart. Close it fully first. TECKNET alarms beyond 2 cm until the parts meet. VOXON starts beyond 20 mm. A sash on the latch can be shut to you and open to the sensor.
If the halves cannot sit together, the frame is the fault. A curved edge stops TECKNET and NICE Home meeting. Do not pack a wedge under the pad. VOXON has no volume slider, so off is the control when it is simply too loud. See the window alarm buying guide.
The 20-minute noise rule, and when to stop
GOV.UK puts an intruder alarm in scope for the council when it sounds continuously for more than 20 minutes, or intermittently for more than one hour. The Clean Neighbourhoods and Environment Act 2005 gives councils powers on audible intruder alarms. Flintronic’s 30-second cycle can still add up if a shock keeps retriggering it. TECKNET runs until the parts meet, so a sash left ajar can pass 20 minutes. Use the off switch.
Call 999 only if you can see a crime. Persistent false trips are for the council. Do not put 999 in an auto-dialler.
Common questions
Why does my window alarm go off in the sun?
Defender reviews describe trips on east-facing and south-facing glass, and the listing has no sensitivity control. This page does not claim a measured heat fault. Switch it off or move it, after you check the LR44 cells. Siting advice for a motion sensor is for a passive infrared sensor, not for a puck on the glass.
Why does the magnetic alarm sound when the window is shut?
The sensor still thinks the halves are apart. TECKNET keeps alarming beyond 2 cm until they meet. VOXON starts beyond 20 mm. A handle on the latch can be enough. If the edge is curved, TECKNET and NICE Home reviews say the halves often cannot meet. Close it properly first. A wedge under a different brand’s contact is not the fix for these pads.
The alarm never trips when I knock. Is it dead?
It may be, or it may be empty. One knock after a fresh arm is the test. Defender, WER and Flintronic say LR44 cells are included. VOXON says four LR44 are included. NICE Home’s AAA cells are not in the box. TECKNET and WOWSEA do not clearly say cells are included.
Can I turn the sensitivity down?
Not on these listings. The vibration pucks do not print a dial. VOXON has off, chime and alarm, and no volume slider. TECKNET’s three levels change loudness, not the 2 cm gap. An adjustable Defender under a different ASIN is a different product. If the pane is too lively, the control you have is off, or a different pane.
How long is a house alarm allowed to sound in the UK?
GOV.UK treats an intruder alarm as a council matter when it sounds continuously for more than 20 minutes, or intermittently for more than one hour. Flintronic stops after 30 seconds and can start again on a new shock. TECKNET runs until the magnet meets the sensor, so an ajar sash can pass 20 minutes. Use the off switch. The 30-second bullet is not the legal limit.
Will the police come because it keeps going off?
Not for an audible-only siren on its own. Ask The Police says these alarms sit outside automatic attendance, and that you call 999 if you can see a crime. Persistent false trips are for the council. A peel-and-stick puck has no police unique reference number. Do not put 999 into a dialler and treat that as a response.
Related pages
Sources
Public UK sources and the amazon.co.uk listings in this comparison. Listings checked 15 October 2026.
- Police.uk: keep burglars out of your property (retrieved 15 October 2026)
- ProtectUK: alarms and CCTV (retrieved 15 October 2026)
- nidirect: securing doors and windows (retrieved 15 October 2026)
- GOV.UK: how councils deal with noise complaints (retrieved 15 October 2026)
- Clean Neighbourhoods and Environment Act 2005, alarm powers (retrieved 15 October 2026)
- NSI: intruder alarm systems (retrieved 15 October 2026)
- NPSA: intrusion detection (retrieved 15 October 2026)
- Avon and Somerset Police: burglar alarms (retrieved 15 October 2026)