Lots of speculation about Geiger counters. Can you link to anyone that actually checked?

F.e. aforementioned SBM-20. Worldwide perfectly known well-tested and long lasting Geiger tube. Anything based on that tube will work fine.

You could easily check your Geiger counter with any radioactive sample, from smoke detectors to thoriated welding tungsten sticks. Geiger tube based counter is a simple device, it is either works, either not. There can't be a situation if it registers background radiation level, but does not detect radioactive substances. Geiger counters easlily could be checked against background radiation level. If it gives you pulses you could just count them and using sensitivity value of used Geiger tube (f.e. from here https://www.gstube.com/catalog/9/) validate your counter. If it gives any pulses for flying through gamma-photons for background radiation, it means it works and it will shurely give you more pulses if there will be more radiation around.

You just can't miss the fact that radiation level become higher than usual background level after certain event. It doesn't have to be deadly or even harmful at all, just if you always had 15uR/h (0.15uSv/h) and suddenly it become 25(0.25) this will inevitably attract attention, and today you will hear a constant scream in social media.

Lots of speculation about Geiger counters. Can you link to anyone that actually checked?

F.e. aforemntioned SBM-20. Worldwide perfectly known well-tested and long lasting Geiger tube. Anything based on that tube will work fine.

You could easily check your Geiger counter with any radioactive sample, from smoke detectors to thoriated welding tungsten sticks. Geiger tube based counter is a simple device, it is either works, either not. There can't be a situation if it registers background radiation level, but does not detect radioactive substances. Geiger counters easlily could be checked against background radiation level. If it gives you pulses you could just count them and using sensitivity value of used Geiger tube (f.e. from here https://www.gstube.com/catalog/9/) validate your counter. If it gives any pulses for flying through gamma-photons for background radiation, it means it works and it will shurely give you more pulses if there will be more radiation around.

You just can't miss the fact that radiation level become higher than usual background level after certain event. It doesn't have to be deadly or even harmful at all, just if you always had 15uR/h (0.15uSv/h) and suddenly it become 25(0.25) this will inevitably attract attention, and today you will hear a constant scream in social media.