There is a switch under the bonnet to detect if the bonnet is being opened. It's easy to knock the switch when working on the car or it may just need adjusted.
Is the car battery in good condition?
Check the elements on the rear screen heater, they are used as part of the "window break" sensor system.
Try pushing the "running man" button just before getting out and locking the car, this cuts out the internal movement sensors thereby eliminating them as the cause.
If you're not sure, just take it to a garage with diagnostic equipment which can read the Alarm Activation Log, this will tell you which circuit is tripping the alarm.
The Vauxhall dealer will probably be most expensive but they will definitely have the equipment.
dara, June 2009
