I use an Aranet radiation sensor[0] that ties in nicely with home assistant. It was more of a fun purchase, and excuse my lack of radiation knowledge, but is it same as those geiger counters or something a big different, I assumed it's similar but slower? They also have other sensors for Radon, CO2, etc

[0] https://aranet.com/en/home/products/aranet-radiation-sensor

Oh I didn't realize that worked with home assistant. It's a little different than a Geiger tube, that device uses a PIN diode and reacts to radiation interactions with the diode itself. Accuracy isn't great for dose but probably decent enough. Sensitivity is very very low, takes a while to get a reading. In theory it should be able to handle high dose rate levels but the spec sheet says it only measures to 1 mSv/hr which is pretty low, I don't know why. Their radon sensor is a different sensor tech, and CO2 and such is standard stuff pretty easy to implement.