E38 alarm fault

[Bigal]

My 1997 E38 - 735i alarm has suddenly decided to go off 'willy nilly'. When i've just unlocked it & b4 putting key in ignition & even whilst driving along (which is tad embarrasing), any idea's please? Also it is not a siren type but a beep beep beep, although I'm told this is a BMW factory fitted possibly european alarm, can any1 confirm this?!?

Eureka!
the AA was going to take the fuse out for the alarm on the n/s under the bonnet for a few seconds? but because a screw was difficult & mite shear he asked if I had an original BMW key with a circle on it & he could do it with that, so the trick it would seem is you follow the handbook for re-initialising the key to the alarm which also resets the alarm & all is wonderful again! this took two minutes or less & charge was zero, albeit I gave him a drink in anticipation.

:'(with ref to my topic last Sunday up to Thursday 18/1/07 everything seemed to be fine after the AA man reset the alarm. Then Friday morn after driving approx 2mls & stopping to pick some1 up I parked & switched off all ok but on my return as soon as unzapping the alarm it started to go off beeping & nothing can turn it off cause its not actually set?!? So I did the 'AA' reset with the key (must remember to wait for the alarm to set b4 going in2 the sequence!) & all was rosy again, until this morning when after a 5ml drive I turned of the engine & bingo the *#@$$*# alarm started again & this time the key thing didn't work(did not remember to wait for the alarm to set b4 going in2 the sequence!) plus the 2nd key at home now suddenly dont work either Grrrrrrr. The only diff at moment is it isn't going off whilst driving? >

MORE INFO
I suppose thankful its not the immobiliser bit at least I can still get around.
My latest info from a dealer mechanic sounds logicalish:
You cant turn/zap it off & it wont help taking out the anti-theft fuses bcos the siren/beep device has its own back-up battery which is located behind the rear bumper (wherefrom bellows the noise); possibility that the battery has deteriated & so prob happens 'willy-nilly', so new siren thingamejig required.
Having said that i'm still a bewildered soul wondering y it went 5 whole days without prob after the AA reset alarm, then twice it happened after i triggerd the zapper to turn off alarm & b4 opening the door then next day nothing until after driving 4mls & it sarts whilst i'm driving along!
i dont suppose damp/water in the o/s reverse light could have anything to do with it?!?