For rough estimations, a smartphone works reasonably well. https://phys.org/news/2014-06-smartphone-detector-app-positive.html https://phys.org/news/2014-06-sm

For rough estimations, a smartphone works reasonably well. https://phys.org/news/2014-06-smartphone-detector-app-positive.html https://phys.org/news/2014-06-smartphone-detector-app-positi... eg https://play.google.com/store/apps/details?id=com.rdklein.radioactivity&hl=en https://play.google.com/store/apps/details?id=com.rdklein.ra...