I use a homemade Geiger counter for RadLog/radmon. About as cheap as it gets if you don't count time, a few transistors, diodes, choke, and a GM tube. My counters are mostly based on this person's ideas: https://techlib.com/science/geiger.html
I also use RadLog for a lightning detector that I made. Pretty simple, and ugly: https://www.getsirius.com/radiation/images/lightningDetector.jpg
Graphs: https://www.getsirius.com/radiation/
