alarm faults
I have a friend who had the same problem with his 525D
I eventually checked the battery in the boot and found that the charge/health indicator was showing black.
It is a sealed unit made by Bosch 90 amp hour
Green...all ok
Black.....insufficient charge
Yellow...replace battery.
The voltage after a short run engine stopped, was 12.1 volts and with the engine at idle speed it was 14.1 volts
If the battery is charged properly the idle speed voltage to the battery from the alternator should be about 13.6
The battery voltage was going below the alarm threshold and it was seen as an intrusion and set off the alarm
This seemed to be weather dependant I.E. temperature related.
Try this and see what you get I think it should be the same in your part of the world.
