Mini One Anti Theft Alarm Issue

That sounds frustrating. I had a similar issue with my Opel a few years back. The security alarm would out of nowhere go off, and it turned out to be a faulty door sensor. Have you checked all your door, hood, and trunk sensors? Sometimes a malfunctioning sensor can trigger the anti-theft system. The immobilizer could also be the culprit. That's a separate system that prevents the engine from starting without the correct key signal. Is the car starting okay?

Thanks for the quick reply! The car starts without issues, so I don't think it's the immobilizer. How can I check the door sensors? What am I looking for?

Regarding the door sensors, I'm not an expert, but usually, a diagnostic tool can pinpoint which sensor is faulty. It could be a wiring issue, a corroded connector, or the sensor itself failing. However, if the error memory mentions something about optical locking, it's very likely the alarm system is coded to activate the indicators upon locking, and something is interfering with that signal. I'd recommend taking it to a workshop with diagnostic capabilities. They can likely recode the system or identify the conflicting signal.

Just wanted to give you an update. Turns out the anti-theft system was coded to activate the optical locking. That's why the alarm went off out of nowhere. Got it recoded at the workshop, cost me 45€. Thanks for your help!