I just had radiation treatment for my thyroid and it has been helpful to know how much radiation remains in my neck and watch it as it dissipates. It provides warning quite well when the phone is near my neck.

I am in an intro to nuclear engineering class and I had to detect the number of gamma counts that a smoke detector would give off. I used this app, thinking nothing of it, but the second I put the tape on the cameras, I was greeted by 0 CPM constantly. It never deviated from that, which makes me believe that this was never a good app, and the reviews saying it was are lying. Either that or it worked on past phone builds but something has changed in the technology. I had to write my report on if this worked or not instead of finding the quantitative values I had to. Just very disappointed in it.

Hats off to the developer for implementing a real measurement tool for radioactivity. Visit his website to see his calibration data, I know that measurements from my iPhone 6p matched my 'real' instrument by detecting faint radiation from my granite countertops.

I doubted the validity of this app, so I tested in the linear accelerator room during my morning radiation therapy. 10 feet off to the side, It worked and actually sounded alarms when the beam was activated.