Only industrial smoke alarms use radioactive sources and even then only some types (you need different types for different situations).
The radioactivity in a smoke alarm is already negligible when you hold it in your hand, never mind when it's mounted on a ceiling.
Additionally the americium-241 used in smoke detectors is mainly alpha decay and a sheet of paper will stop it, the remaining radiation that is dangerous is gamma and it's exposure is so far below annual average background that you might not even bother. Flying in a plane will expose you to a thousand times more radiation.
The radioactivity in a smoke alarm is already negligible when you hold it in your hand, never mind when it's mounted on a ceiling.
Additionally the americium-241 used in smoke detectors is mainly alpha decay and a sheet of paper will stop it, the remaining radiation that is dangerous is gamma and it's exposure is so far below annual average background that you might not even bother. Flying in a plane will expose you to a thousand times more radiation.