Wish I'd found this forum sooner!
I've got a 1998 Omega 2.5 CD and luckily I don't have the usual problem of the alarm going off constantly...
Mine won't set or lock the car when I press the fob, the alarm 'self-diagnostic' is showing no faults (when alarm is set using the key in the door: red light on solid for 10 secs, then flashes after), I've tried a new battery in fob, still nothing, tried it in programming mode in case it had forgotten everything, still no joy. Checked all doors and boot are closed, tested power sounder and alarm horn under scuttle, both work fine.
Also, if I lock it with the key the alarm will set and CL works fine, but if I unlock it with the key the alarm goes off until I put the ignition on, which my neighbours don't really appreciate at 5:30 every morning, so until I have some luck with it the car remains OPEN ALL NIGHT on the street outside my house

Any help at all is massively appreciated.