Doors, windows & security
Burglar alarm crying wolf? Calm it down
An intruder alarm that sounds when nothing is wrong trains the whole street to ignore it, which is the one thing an alarm cannot afford. Most false alarms trace back to a short list of culprits, and most of the list costs very little to put right.
By the Tickover team · Published 26 January 2026 · 4 min read
What sets an alarm off when nothing is there
An alarm system is a chain: motion sensors in the corners (PIRs, watching for moving warmth), contacts on the doors, a control panel doing the thinking, a backup battery for mains blips, and a sounder with no sense of occasion. A false alarm means one link in that chain told a lie, and the pattern of the lying usually names the liar.
| Pattern | Likely culprit | First move |
|---|---|---|
| Sounds around 2–3am | Backup battery past its best | Book an engineer battery swap |
| One PIR trips repeatedly | Spider or insect on the lens | Dust the sensor, clear webs near it |
| Trips on windy days | Draughts moving post or coats | Brush-seal the letterbox, clear sightlines |
| Trips when next door drills | Vibration sensors set too keen | Engineer retunes the sensitivity |
| Door zone faults in cold snaps | Door contact gap has widened | Realign the door and contact |
| Keypad grumbles about a zone | Wireless sensor battery low | Replace them all in one round |
The small-hours performance usually has the same plot. Mains power blips briefly overnight, the panel leans on its backup battery, and a battery past its prime sags far enough to register as a fault or tamper. Cold nights make weak batteries weaker, which is why winter gets the encores; the same physics is behind a smoke alarm’s 3am chirp.
Fixes within reach of a step ladder
Calm it down, in order
Note which zone triggered
The keypad or panel log names the zone. One repeat offender is a sensor problem; every zone at once points at the panel or its battery.
Dust the PIRs and evict the spiders
A dry cloth around each sensor and no webs within arm’s reach. A spider strolling across the lens reads as a warm intruder, and autumn is their touring season.
Kill the draughts in the sightlines
A letterbox without a brush seal, a swaying coat on a newel post, a stray helium balloon: PIRs watch for moving warmth, and draughts supply the movement.
Check the door contacts
A door that has dropped or swollen widens the gap between contact and magnet until the zone flickers. The five-minute hinge fix usually closes it.
Change wireless sensor batteries yearly
Battery-powered sensors warn before they die, rarely at a convenient hour. Change the lot in one round rather than one funeral at a time.
The panel and the bell box are not DIY
The control panel and the outside sounder run on mains with backup batteries inside, and the bell box lives a ladder-length up the wall. Replacing those batteries means opening mains-powered kit, so it is a job for an alarm engineer or a qualified electrician, and usually a quick one within a service visit.
A service every couple of years keeps the rest in tune: batteries measured, contacts tested, sensitivity adjusted, event log read properly. Monitored systems earn it sooner, because repeated false alarms can see police response downgraded, which defeats the point of paying for monitoring.
What calming it down costs
Panel battery, part only
sealed 12V type
Engineer service visit
battery swap often folded in
Typical UK ranges, mid-2026, as a guide only. Your home, your area and the job itself all move the number — always compare real quotes.
Keep the street on your side
The false-alarm prevention round
- Test the alarm monthly, warning the household first
- Dust PIR lenses and clear webs each season
- Keep post, plants and coats out of sensor sightlines
- Replace wireless sensor batteries once a year
- Book an engineer service every two years
- Recheck door contacts when any door starts sticking
- Keep keyholder names and numbers current
- Set the alarm every time, not only for holidays
False alarms also spend the one thing an alarm exists to buy: attention. Once the street stops looking up, the loudest box on the road is decoration. A video doorbell makes a useful witness alongside a calmed-down alarm, and both earn their annual once-over in the security walk-round.
Not sure what you’re dealing with?
Still crying wolf after the spider hunt? Tickover Self-Diagnose narrows it to the sensor, the battery or the panel, and can line up a vetted alarm engineer for the rest.
Quick answers
Why does my burglar alarm go off at 3am for no reason?
Overnight mains blips hand the system to its backup battery, and an ageing battery sags under the load, which the panel logs as a fault or tamper. Cold makes it worse, so winter nights are peak season. A new panel battery ends it, fitted by an engineer because the panel and sounder are mains powered.
Can spiders really set off a burglar alarm?
Yes. A PIR watches for moving warmth, and a spider crossing the lens at point-blank range looks enormous to it. Webs swaying in front manage the same trick in a draught. Dust each lens with a dry cloth every season and clear webs within a metre, and the phantom intruders usually retire.
How often should a burglar alarm be serviced?
Every couple of years for a bells-only system, and yearly where the alarm is monitored or your insurer requires it. A service checks the panel and sounder batteries, sensor sensitivity, contacts and the event log. Between visits, test it monthly and change wireless sensor batteries annually, all in one round rather than piecemeal.
How long can a burglar alarm legally ring for?
Modern external sounders are designed to cut out after roughly 15 to 20 minutes, though the strobe keeps flashing and the internal siren may continue. A persistently sounding alarm can be treated by the council as a statutory noise nuisance, and in some cases silenced at the owner’s expense, so a nominated keyholder is more than a courtesy.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
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