C1 Anti Theft Alarm Issue

Whoa, phantom alarms are the worst! Sounds like a coding glitch. Any recent work done on the electrics? Did you check the battery? A weak battery can cause all sorts of weirdness, including triggering the alarm. Or it could be a dodgy alarm sensor. Has it been raining a lot where you are? If so I'd check the alarm sensor connections for corrosion.

Battery's testing fine, so I am really suspecting sensor connections. Is there a common sensor location I should prioritize checking before I tear the whole car apart?

Yeah, if the battery's solid, definitely dive into those sensors. Given it's activating the optical locking, I'd put money on it being a coding issue in the BSI (Built-in Systems Interface), triggering the alarm when it shouldn't. That said, without the right tools, it's tough to diagnose yourself. I'm leaning towards a trip to a garage with the right diagnostics. They should hook it up and be able to tell what sensor is firing and if the BSI is coded correctly, good luck!

Yep, you called it! Ended up being exactly that. Took it to a garage. They recoded the alarm system so that it stops the optical locking. Cost me 45€, sorted now, thanks for the help!