how do i disable the car alarm ( vectra 2.5 v6 r reg )?

Easier and cheaper to fix the fob.
Have you tried fitting a new battery in the key and re-syncing it?
To re-sync, turn ignition until the dash lights come on but dont start the engine. Press the lock button on the fob. The doors should lock and unlock. The remote should now work the locks and alarm as normal.
If the fob is broken beyond repair it will be easier and cheaper to buy a replacement than to disable the alarm.

elton
September 2009