DS3 Door Lock Failure

Sounds like a faulty door contact signal, which would explain both the locking and alarm issues. Have you checked the cable or plug connection of the component? That's a common weak spot.

I haven't checked the cable or plug connection, no. Is that easy to get to? Or am I better off just taking it to a shop? Don't want to make it worse.

It can be easy to get to, depending on your experience. But if you're not comfortable poking around with the car's electrics, you're probably better off having a workshop take a look. A faulty door contact signal definitely sounds like a cable or plug issue, so you're on the right track though. Could be a cheap fix.

Thanks for the advice. Took it to a local mechanic, and you were spot on – faulty door contact signal, cable connection was the problem. 95€ and it's all sorted. Appreciate the help!