Basically just a tripwire based switch made from stuff lying around the house. Can also be used as a remote switch for things you don't want to be next to when you turn them on.
Step 1: Tools and stuff, you will need...
Thin copper plate
Thin card/ plastic
String/ invisible thread
Device you want power
Pen knife or some other kind of cutting implement.
Step 2: Constructing the switch.
Cut the copper plate to size. You need two pieces, roughly the same size, big enough to stick to the inner jaws of the peg and have some hanging out the side to attach the crocodile pegs to. It's best to have some stick out of one side on the top and the other side from the bottom.
Step 3: The Trip gizmo.
Get your piece of card/ plastic and cut to a decent size. Big enough to seperate the jaws of the peg without the copper pads touching each other.
Poke a hole through one end and tie the tripwire through it.
Step 4: Finally there.
Insert the card/ plastic break into the peg jaws. Attach the crocodile clips to the pads. The other end of the clipped wires, it is up to you. Light or sound devices will work with this.
You can either wedge it under something , but I put a string through the center of the spring to anchor it to something solid.
Simply put, the card acts as an insulator an gets pulled out when the tripwire is.. well, tripped.
The copper makes contact and the whole thing acts as a switch. Done.
Works well with my Quick and Dirty Squib instructable (but only when used with caution). Check it out, NOW.