Golf 4 Alarm: Door Open Issue?

Hello.

I've been having a problem for a while now where my Golf doesn't seem to register when the passenger door is open.
So, when the door was opened, the interior lights didn't turn on.
But what's even worse is that if, after unlocking the car with the remote control, only the passenger door opens within the first 30 seconds.
Then he locked it again, and the alarm system went off.

For the past few days, my car hasn't been recognizing when the driver's door, passenger door, or trunk has been opened.

Now I'm wondering why he doesn't notice that the doors are open, but the alarm still goes off.

I haven't found a switch on the door frame. Is it possible to install one myself, or what kind of costs should I expect?

Thank you in advance.

JL

The switches are located inside the door locks.

Do you perhaps have an ultrasonic interior monitoring system?
"He" then looks out through the open passenger door and notices that something is moving outside.

You can identify them by the button located at the very bottom of the left B-pillar.
Or you know what US sensors look like.

First of all, thank you for the reply.

My Golf does not have an interior monitoring system.

So, am I understanding correctly that the door locks probably need to be replaced?
'How much will it cost approximately?'

Or perhaps someone else has an idea?

You're welcome... JL

Front door locks with central locking: €108 each. Rear door locks: €103 each, including tax.