As a contractor a few years back I built a massage parlor, just a few rooms and a common shower, each rooms door had a mirror on the inside and on the hall side hung a picture, if you moved the picture to the side it revealed the back of the one way mirror which you could look through to see inside the room, each table had a button under it that the attendant could push to turn on a light at the front counter to say she had trouble , before they came into the room to see what was going on they could move the picture and make sure the girl had not pushed the button by mistake, didn't want to scare the customer away if it was a mistake, next time you go into a room and there is a picture on the door look to see if there is a mirror on the other side, you never know who is watching!!!!!

