There are various Geiger counter apps that work by taping something over the camera such that it's blacked out, and then measuring excitement of the CMOS sensor

There are various Geiger counter apps that work by taping something over the camera such that it's blacked out, and then measuring excitement of the CMOS sensor by gamma rays. These apps have been found to work but only for gamma, sensitivity isn't great, I have seen it described as an "am I already screwed?" detector app.