I just thought of something that used to happen; I can't believe that I forgot about this!
I used to be the Executive Director of an art association. Our building was an old historic home that was in disrepair when it was donated to the association. Many artists and volunteers worked countless hours making it a beautiful gallery and workshop space. There was an alarm system that included motion detectors, exterior door alarms and several interior contact door alarms. There was also an iron bar door for extra security on the front door. To arm the system, the contact doors had to be closed or the alarm could not be set.
If the alarm went off in the middle of the night, the alarm company would call me and tell me which alarm had tripped, and alert the police. Now granted, the motion detectors could be set off if a spider or some other bug walked across the 'eye' or if something moved in the room. Every once in a while, the front door would open due to wind or dry conditions but the iron bar door kept the building secure. Many of the times, the alarm that was tripped was the interior contact door that led to the 'Members Gallery'. There was absolutely no way for that door to open without turning the door knob and pulling to door open. Absolutely no way. Now mind you, I usually got there before the police (even though I lived 20 minutes away) and sometimes the police never got there. I had to go into that big, old and dark building to close that door to re-arm the alarm. This was usually between 3:00 and 4:00 a.m. I always knew when I got there what alarm had gone off and had a 20 minute drive to think about it! Nothing creeped me out except that Member's Gallery door. I guess there were some hard working artists on the 'other side' that wanted to make sure that we didn't get to "big city snooty' and were keeping that passageway into 'their' gallery open...
I got an alarm call probably at least once a month, and it was never a break in...but something set off those alarms...
True story.