Parts of this idea are being used for other purpose but here it is. Suppose you are in you bedroom or working on something interesting and you don't want to be interrupted when suddenly someone knocks on your door. The idea is to build or assemble from already present device a transmitter and reciever than can control the lock in the door thru a powerful magnet coil (or an alreday present mechanism can be found i the market-by mechanism i do mean the hole door mechanism). The...