A Geiger counter (Geiger-Muller tube) is a device used for the detection and measurement of all types of radiation: alpha, beta and gamma radiation. Thanks to an ingenious German physicist named Hans Geiger, we've all heard the sound of radioactivity. It's just as well we do have Geiger counters because most radiation (radioactive particles and energy) is extremely harmful to living things, completely invisible, and very difficult to detect in other ways.