Alarm going off whilst driving ... Help

Yes I've done lots of searching but can't find any answers
300 TDI E.S
Went out today and whilst driving the alarm siren started going off, got out of me car no lights flashing just the siren blaring away.. turned off the ignition and used the fob to lock doors etc then unlocked it and the immobilizer wouldn't let me start the car did the same again and me car started,drove off and the siren was going off again but wanted to get home so just drove it (lots of strange looks off people)
Over the weekend the alarm went off twice whilst parked on the drive 03.30 waking me up but I didn't realise it was me car as no flashing lights and again in the afternoon
Any ideas
Thanks in advance

As you have a battery backed up sounder any loose connection between the alarm ECU and the sounder will activate the sounder, also a faulty ECU of sounder itself may activate the sounder, this is assuming the battery in the sounder is still ok.
If your lucky removing the plug on the sounder to check it is clean should activate the sounder if the battery is ok, doubtful though as mine packed up about ten years ago.

There is an alarm test sequence u can do this is detailed in Rave manual.