Douglas Harper's Etymology Dictionary
1924, for German physicist Hans Geiger (1882-1945), who invented it with W. Müller. The surname is literally "fiddler."
Wikipedia
The Geiger counter is an instrument used for measuring ionizing radiation used widely in such applications as radiation dosimetry, radiological protection, experimental physics and the nuclear industry.
It detects ionizing radiation such as alpha particles, beta particles and gamma rays using the ionization effect 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 detection instruments.
The original detection principle was discovered in 1908, but it was not until the development of the Geiger-Müller tube in 1928 that the Geiger-Müller counter became a practical instrument. Since then it has been very popular due to its robust sensing element and relatively low cost. However, there are limitations in measuring high radiation rates and the energy of incident radiation.
Usage examples of "geiger counter".
But ever since I walked into this hotel with my Geiger counter I couldn't wait to find old Sam's room and the rock collection he told me about this morning.
By sending her back on board, and with the Geiger counter, he was putting her in double danger.
He took a final puff, blew it at the Geiger counter, and put it out.