vacumn/alarm questions-HELP
 

1987 300sdl. 290k and climbing
About two months ago alarm went off for no reason. I tracked what I thought was wrong and replaced driver's door vacumn/switch in door. Seemed to work until now. Just got call from Wife, alarm is sounding (in car, not wife) for no reason...car was unlocked in garage overnight and she opened door; alarm went off and would not shut off w/ key.

Any help would be appreciated..should I replace the switch/vacumn in the passenger door? Would this be a symptom of vacumn leak somewhere? How do I diagnose this?

update
 

Ok, had discussion locally w/ tech. He says motion detector might be bad. Any ideas where that is?

Think it is in the trunk.