“We’ve all seen them, they’re welcome mats for outside your front door that make spooky sounds whenever a trick or treater comes knocking. I’m going to show you how to make half of this, so that you can use it for lights, sounds, or some kind of motor powered device (like a skeleton that waves when you step on the plate). Pressure plates work very simply, there are two hard pieces (the plates) with conductive material on each one (aluminum foil) and some kind of spring in between them (sponge). Wires are attached to each piece of conductive material, so when the two plates touch each other (someone steps on it) a circuit can be completed..”