The circuit above is the Halloween Spooky Audio Trigger, it has a door contact sensor connected to it and when it detects that the door has opened it waits for a short time before scaring the pants off your trick or treaters with some spooky sounds! The detection of the door opening is actually the simple part, the more complex part of the Halloween project is how the Nerd Kit is programmed with the audio in a fashion that can fit into the limited space available.