... and the engine keeps running?? Or does it turn off when the switch is opened?
PS: What do you think about it?
'However, it's too expensive for my car (approximately 370 euros without installation), but for a truly valuable car, I would buy it immediately.' http://www.kfz-diebstahlsicherung.de/autotypen.html
But the thief wouldn't be able to see that from the outside.
It definitely needs to be an alarm system that prevents the thief from breaking in in the first place.
Perhaps it's really an ultrasonic sensor, like in the A3. You would also need the corresponding control unit and the central locking pump to do the conversion (i.e., replace everything).
It will be expensive, though.