Eighty years ago that was the case. Fifty years ago that was the case in many places. Today that is no longer the case. There are very robust and effective sensor networks in any and every location where there exists any possibility of a radioactive concern.
The point stands - for the individual it is very reassuring to be able perceive a danger. And not all radiation sources have masses of alarms near them. Hospitals for example don't put detectors everywhere and they have some very nasty radiation sources.
