The Geiger Counter (alternately known as a Geiger–Müller counter) is an instrument used for measuring ionizing radiation. The principle behind a Geiger counter is that a tube filled with an inert gas is charged electrically allowing for the detection of radiation by sensors. It detects radiation such as alpha particles, beta particles and gamma rays using the ionization produced in a Geiger–Müller tube, which gives its name to the instrument. In wide and prominent use as a hand-held radiation survey instrument, it is perhaps one of the world's best-known radiation instruments. Very little is known of the Professor's implementation, but it is known the Professor barely got it built because Gilligan kept disturbing him and the Skipper during it's delicate construction. No tubes or an electrical source is seen, but a measuring scale can be seen on the face of his counter. It is unknown how exactly the Professor calibrates his Geiger counter to ensure his readings are accurate.
- Bamboo (housing, tripod)
- Metal components (various)