Thank you for the replies.

History: I have been having trouble activating and de-activating the cobra alarm/immobiliser system for the past 2 months. I thought it was faulty radio keys, so i bought a new key battery for both of them. Still problems and I just guessed it may be a faulty switch/contact within the radio keys (they seem old). Reason: the green button (immobiliser/central locking) only worked 50% of the time, but the yellow panic button seemed to work 100% of the time. So, I go to Holland, Italy and then France with work for 2 weeks, leaving my car parked outside at home in London. When i return, I try to gain access to the car, but no joy. Now, the yellow panic button doesn't work. When I open the door with the manual key, the alarm should trigger (motion sensors). I believe my alarm system has it's own battery back-up: perhaps this has failed? The way my immobiliser works, is that when it is immobilised, nothing should come on when i turn the key, no dome lights, nothing. However, what is also odd, is that the red LED on the dashboard is off (when the car is immobilised, the red LED should be lit on). So, I'm guessing it is the alarm system battery that may be dead.

Sorry for the long post! I'll call a local alarm fitter and get them to figure it out for me, though any other helpful suggestions would be greatly appreciated.

Thanks,

Phil