More and more false radioactive alarm was set off in US due to the sensitivity of the radioactive censor. Apparently many patients in US undergo treatment that leaves a small amount of radioisotopes in their body, that small amount is enough to trigger any handheld radioactive scanner. Quotes from Reuter,
"Nearly 60,000 people a day in the United States undergo treatment or tests that leave tiny amounts of radioactive material in their bodies, according to the Society of Nuclear Medicine. It is not enough to hurt them or anyone else, but it is enough to trigger radiation alarms for up to three months. "
(Link) Although US medical people claims that those radioisotopes is too little to cause any serious harm to the patient and environment, but just thinking about the amount of x material present around us is a bit scary.