Door lock confirmation
just to let someone know they should use a key to start this vehicle
not a screwdriver.

nothing to do with an alarm , although its a warning i suppose
Passive Anti Theft System
There is some confusion about what PATS is, and what it does. It is not part of the central locking or the alarm system, . It is designed to be completely transparent so that it requires no action at all on the part of a driver, and always remains active, even if the doors are left unlocked and the alarm is off.
The PATS system was first a separate module mounted beneath the dashboard, and later became part of the engine management system, and is connected to a transceiver mounted around the ignition barrel. When the ignition key is not present, PATS disables all of the EEC V engine management, and on some models the starter as well. The PATS receiver awaits an ignition key with a transponder (could also be a little red tag mounted in the key) which matches the code that PATS recognises. This is the clever part: even if a key is an exact physical match with the ignition lock and the key is turned, PATS checks the transponder code and if it is not recognised the engine is dead.
So the spotty dork who breaks in to steal the car smashes the steering shroud and rips away the electrical connection at the back of the barrel is wasting his time. The ignition switch itself will turn, but the engine management system has not received the OK from PATS and the engine remains stubbornly silent.





