There was a story mentioned here a few years ago about a heart patient who underwent some sort of nuclear medicine procedure and was actually detected by cop driving down the street who had some sort of radiological detector in his car.
The cop ended-up pulling him over because of the alert registered by the device.
When I had radioactive iodine ablation of my thyroid, I was given a letter from the hospital stating that I was radioactive for medical reasons, but was still warned I couldn’t fly for some time, and risked alarms in some places as well. Mostly I felt way to crappy to worry about setting off alarms, but I was radioactive for weeks afterwards.