The Geiger Counter is a ship part found in Pikmin. It is one of the vital parts of the S.S. Dolphin and Captain Olimar is unable to leave the planet without it.
How to Get
The Geiger Counter is in one of the three Burrowing Snagrets of the area, having the Whimsical Radar can be useful to identify which Burrowing Snagret hold it instead of killing the three.
"It's the Geiger Counter! Every spaceship needs one of these, but I don't actually know what it's for. Every once in a while, it goes wild and lets out a lot of noise, but I never pay much attention to it, so it doesn't do me much good. I really should read that instruction manual one of these days!"
"This noisy gauge is always letting of spontaneous clicks and buzzes. It can be kind of annoying."
A Geiger Counter is a device used to measure radioactivity in a given area. The clicks and buzzes Olimar mentions is the Geiger Counter reading the amount of radiation which means that PNF-404 might have been exposed to intense radiation in the past.