Geiger counter

The Geiger counter was invented to detect and record energetic particles emitted by radioactive substances. A single subatomic particle, on entering, would set off an avalanche of ionization, producing a momentary electric discharge. The clicking of such a Geiger counter gives us information that our senses cannot give us.
 Johannes Hans Wilhelm Geiger Germany 1908 Geiger counter

The Geiger counter was invented to detect and record energetic particles emitted by radioactive substances. A single subatomic particle, on entering, would set off an avalanche of ionization, producing a momentary electric discharge. The clicking of such a Geiger counter gives us information that our senses cannot give us.