What are these switches called?

Question

Well like i have seen at many places..lights go on when we enter a room and then they go off when we leave from the room automatically. What are those switches called?

Answer 1

Are you talking about lights connected to a motion sensor?  

Answer 2

automatic motion sensor lights they have them at my moms job

http://www.smarthome.com/2520W.html

well this one is expensive