Fault
Car alarm goes off by itself: possible causes
An alarm that goes off by itself almost never does so without reason. The system is measuring something — the question is what.
The most common causes
- Moisture in the module, siren or a contact
- Oxidation on terminals, splices and earth points
- A shock or ultrasonic sensor that has become too sensitive
- A door or boot contact that keeps sticking
- Voltage drop from a weak or ageing battery
- Loose connections left from an old installation
Why the pattern matters
Does the alarm mainly go off in rain, in heat, after standing for a long time, or right after driving? That pattern often already points towards moisture, temperature or battery voltage. So mention as much as possible about when it happens.
What you can check yourself
- Do all doors, bonnet and boot close fully?
- Has the battery been tested recently?
- Was anything done to the car shortly beforehand?
- Does it happen in one place or everywhere?
Frequently asked questions
Questions about this service
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Tell us which vehicle you have, exactly what's happening and where the car is. You'll get honest advice on what's technically and economically sensible.