Dear experts,
I have a 2001 Omega 2.6 V6 CDX (Y Reg) Auto. Fantastic car - as you well know. 8-)
I seem to have developed an alarm fault over the past 24 hours.

Apart from the alarm refusing to activate the ONCE, months ago, never had a problem before. Now, when I park the car after a journey and 'blip' my central locking (which arms the alarm) very soon afterwards (about 5-10 mins) the alarm goes off. If I do not cancel it with the = button on my key fob, it will keep reactivating the alarm virtuously continuously - I can tell this as there is a very slight pause between alarm cycles, but it is as good as continuous.
To stop this from continuing, I have to press the cancel = button again and again until it stops setting off the alarm. E.g. Alarm. I cancel. Immediate alarm again. Cancel. Same again, up to half a dozen times or a little more, and then it's fine. Once I've done this and it has stopped, I can even lock and unlock the car (and boot separately) without incident, but the next time I drive off and park, same problem.
I have tried different variables: e.g. locking it with the key (this still seems to arm the alarm), turning off the internal alarm from the dash, but still it goes berserk shortly after parking.
I should point out this has only happened the past 24 hours! However, it seems to be here to stay!
I spoke with my local garage chap (trusted friend of the family and Omega aficionados) who put me in touch with his alarm chap - but he said it would be best to take it to Vauxhall with my card that has all the numbers on and get their computer to read the diagnostics. I fear expense - when the words 'main' and 'dealer' are used in the same sentence.
Therefore, has anybody had this problem, any advice for s.o who is not very technical (!), or / and am I better off going to my local Vauxhall dealer and preparing a large cheque?!!
Many thanks,
Jeremy.
Jeremy Hanshaw