See the world in a whole new light by converting your old webcam into an infrared camera.
Webcam sensors are sensitive to both visual and infrared radiation. They come with a filter that blocks out the infrared so your camera just picks up light. Though this is fine for most uses, it presents an opportunity for a great hack.
Carefully disassemble your webcam and unscrew the lens. Find the small glass filter, which will have a coloured tint when you look at it from certain angles. Replace this with a small strip of fully exposed film negative. This will block out most of the visual light, but let the infrared through.
Reassemble your camera and see how it looks. TV remotes and UK £5 notes are particularly good subjects.