When a tenant reports the house alarm going off for no reason
A landlord's guide to false activations across rental properties
Landlords managing one property or a small portfolio often get the same call from a tenant: the alarm went off in the middle of the night, or while the house was empty, and nobody can work out why. Before assuming a break in attempt or a faulty system that needs replacing, it is worth working through the genuinely common causes, most of which are cheap and quick to fix once identified.
This guide focuses specifically on situations where an alarm triggers with no apparent intruder, no forced entry, and no obvious explanation from the tenant. It covers the usual suspects, from insects and draughts through to detector age and expiring components, and gives landlords a practical way to talk a tenant through basic checks before booking an engineer.
Because tenants are not always familiar with the property's alarm system, clear instructions matter. A short written note left at the property, or sent by text, covering how to silence a false alarm and what not to touch, can save both a stressful night for the tenant and an unnecessary emergency call out fee for the landlord.
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The Usual Culprits
Insects inside the detector casing
Spiders in particular are drawn to the warmth inside a PIR housing and their movement across the sensor lens can trigger a false alarm, especially in warmer months.
Draughts and moving objects
Curtains, blinds, balloons or hanging decorations moved by draughts from an ill fitting door or window can pass in front of a motion sensor's field of view.
Ageing or failing PIR sensor
Detectors generally have a useful working life of around eight to ten years, after which internal components can become erratic and prone to false triggering.
Low sensor battery
A weakening battery in a wireless detector can cause intermittent, unreliable readings before it eventually fails outright, sometimes registering as a false trigger.
Recently disturbed furniture or fittings
New furniture, a mirror, or even reflective surfaces introduced into a room can interfere with how a PIR reads movement and heat within its zone.
Loose or ageing tamper switch
A cover that does not sit perfectly flush, or a tamper switch that has loosened over time, can trigger what looks like an alarm but is technically a tamper event.
Try These Before You Book Anyone
Ask the tenant which zone triggered
Most keypads display a zone number or name at the time of the alarm. This single piece of information massively narrows down the likely cause before anyone visits.
Rule out weather conditions
Strong wind can move curtains, hanging decorations or loose blinds in front of a PIR sensor, and draughts under doors can occasionally trigger sensitive detectors near entrances.
Check detector housings for insects
Spiders and small insects inside a PIR housing are a very common and often overlooked cause of repeated false triggers, particularly in summer months.
Confirm nothing was recently moved
New furniture, a plant, or even a helium balloon left in a room can obstruct or reflect a detector's field of view enough to cause a false trigger.
Ask about recent battery warnings
If the keypad showed a low battery message in the days before the false alarm, a failing detector battery may have caused an erratic trigger.
Check the tamper indication
If the keypad shows a tamper alert rather than a standard zone alarm, this points to a different cause, such as a loose cover or damaged cable, rather than motion detection.
Log the date, time and zone of each event
A simple written log across repeated incidents makes it far easier for an engineer to spot a pattern when they do eventually attend.
The Point Where It Needs an Engineer
Keeping it from coming back
A brief annual service visit, ideally scheduled between tenancies, will clean detector housings, check batteries and confirm sensor positioning is still sensible for how the room is furnished. Providing tenants with a simple one page guide to the alarm on move in also reduces panicked calls and misreported faults.
Questions We Get Asked About This
When a tenant reports the house alarm going off for no reason: common questions
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