I got my hands on a Geiger counter the other day. It’s a GMC-300E, they’re affordable, and the build quality is decent.
The device has an unlocked serial interface via USB, and the manufacturer has published the protocol documentation. This allows you to download the logged data and read life data from the Geiger-Müller tube, and with the 320 model also from the temperature sensor and gyroscope.
This is a quick guide on how to access the GMC-300E serial interface in C#.