In my case (96 850 sedan, 124k miles) which just started yesterday, the dang alarm comes on/off intermittently...whether the key is in the ignition or in the house! The mights don;t seem to be bothered...I will say that the remote does not work when the beeping occurs, and that the slghtest thing, (turn signal, braking) causes it.

Drove to the Vovlo shop today, the senior Tech said he sees this once in a while, it seems to be a "relay" and not a fuse (and that's all he said, didn't seem too familiar with the issue). He pulled the cord out of the alarm, said to tie it with electrical tape to some other wires (so it wouldn't fry if it were to hit the engine), and come in when they have time...Xmas week and all that...it remains unclear if my version of the problem also is draining the battery...

Let me know if they devise a solution for you. I will do likewise. Good luck.