An IR transmitter and IR receiver placed at either side of a doorway sends and receives IR stream. If the beam is broken, a buzzer will beep or a relay will trigger. Please read "readthis!.txt" for all information.
Everything included, source, assembler, programmer, and Receiver and Emitter datasheets in docs folder.
If you find a better way to do this, please message me here at avrfreaks, nick is newbie123.