Cold War dosimeters, by Bendix. These are pen-sized radiation detectors that require no power. If you hold them up to the light and look through them like a telescope, you see a tiny little radiation gauge with a thin wire indicating the current setting. Exposure to ionizing radiation moves the wire. So you’d measure your starting reading (say, “5 Roentgens”), and then wait an hour, then check again (say, “6 Roentgens”) and then you’d know that wherever you had been had exposed you to 1 R/hr of radiation (radiation workers in the US are allowed to have about 5 R per year exposure, to put the numbers in contrast; about 500 R in a short dose will kill you, 100 R will make you quite sick, and below that you are just adding to your lifetime cancer risk by a small amount). They are entirely passive and require no electricity or anything to operate — very low-tech high-tech.