The remote central locking and immobiliser are two completely seperate functions.
The immobiliser has a ring aerial around the ignition switch which sends a pulse to a transducer chip in the key. It reads the code from the transducer and, if it matches a code in the system, it will allow the car to start.
When you press a button on the central locking keyfob it sends a coded radio signal to the central locking unit in the footwell. If the code (which changes every time you press the button) is accepted by the system the doors will lock/unlock and the alarm (where fitted) will switch on/off.
The one has absolutely no connection with the other, so I cannot understand what this garage has done.
reddlett
September 2011