E39 alarm keeps going off

[Invertigo]

Asking for my dad, as this is bugging him quite a bit at work!

Basically, whenever he locks the car (2000 528i), the alarm seems to go off every hour or so for no obvious reason. Even when it's parked on the driveway at home, well away from the road (which is quiet anyway) it keeps going off, yet never happens at night (I don't know if thats relevant).

Any known causes of this, or is it a case of a slight electrical fault somewhere thats going to be a pain in the arse to locate? Was thinking the regularity could be a sign of a low battery?

Any help would be great

 

[Richie]

My E39 used to do the same and it was indeed because of a shoddy battery. Changed it, problem fixed. This might not be the case with yours but you never know.

 

[Joe T]

It's unlikely to be this given the time of year, but my e46 (which is probably similar, but I couldnt be 100%) had a similar issue in warm weather. The bonnet would expand, lift up ever-so slightly, and release the alarm switch for the bonnet.

There are two solutions:
1 - tape the bonnet alarm switch down
2 - put a small rubber grommet (available from BMW I believe!) on the underside of the bonnet to ensure it firmly pushes the switch down