Whenever your exploring or scavenge deep in the wasteland zones you should have an Geiger counter with you. This is an practical model small and you just fit it on your belt. When it starts to go off, get the hell out of there.
Made from an old voltmeter, the cathode made from I think are a transistor (but I would say a internal piece from a computer) that I burnt with linseed oil for that reddish brown black finish and some wire from I think was a ham radio microphone. The radioactive label I took from the backside of a smoke detector.
If you like Post Apocalyptic gear check out the rest of my gallery [link]