We have a doorbell downstairs.  We can't hear it upstairs so I put in a sensor inside the doorbell that will set off several others in the house.  It's activated by sound. Apparently in the middle of the night there was a mass suicide in our kitchen.  It set off the doorbell.  The wife and I agreed it was probably just the cats playing and went back to sleep. This is what I woke to a 3:30.