The usual fault is the window glass - the system runs on a closed loop ie the wire runs all the way around up the wire through the glass and back down the wire
You can access the wire inside the panels at the side of the car and cut them and connect them together ( this is what vaulhall do ) unless you want new glass installed
Your glass wont then becovered by the alarm but the sensor in the car will still work anyway .
Mark
October 2007