My wife had a over active thyroid problem and the doctors recommended taking the radioactive iodine tablets to kill off her thyroid, then take hormone replacement pills for the rest of her life.

But when she told the doctors that she planned to travel to the Philippines in the next few weeks, he advised her not to have the procedure. Reasoning was that she would set off all kinds of alarms at the airport, plus putting at risk any passengers sitting near her on the plane.
The doctor said, that they usually give some document to patients that explains the reason for their high radiation, so that if they get detected, they would have an explanation.

I started to think what device at the airport checkpoint detects radiation?
What alarms would she have set off?
I understand that if would not be right to put at risk any fellow passengers if one was emitting radiation, but is there really something they do at a checkpoint that can detect radiation coming off of people?