Those thing that have some chemical agent that smells like a rotting corpse that gets release if someone is trying to break in your house.  I am not sure if how hey are set off or what.  

Read some thread a while back where a guy talked about how he had a room w/ his gun safes in it & a sign on the door that said like "warning, this room is under 24 hour monitoring, do not open this door"  and some friend of his wife was at a party and opened the door anyway & set off the sink bomb & ran everyone out of the house.

I think he said the chemical degraded to nothing after like 2 days.