Pluck a hair from your head.
Dip hair in the sugar glue
stick the hair on the door so it spans the door and door frame.
The sugar glue is invisible and no one notices a single hair glued to the door and door frame. If anyone opens the door, the hair falls off and you will know someone opened the door.
I suspect my roommate may be going into my bedroom in our condo when Im away. It has a lock on it, but the construction is bad and you can easily break into the rooms using a card. I dont notice things are amiss when I come home, I think hes being very careful to leave things as they are. Ive been trying to think of a way to set up a trap in my room that will prove my suspicions. Im not looking for a lecture on why Im living with a person who I suspect of such behavior and I understand that a confirmation would be automatic grounds for moving out. Hence, why Im here. But, I am a poverty stricken individual and moving would be very painful so I want to be sure before I make any moves. Any help?? Thanks!