The radiation given off by the Americium as it decays ionises the nitrogen and oxygen molecules in the air space between two oppositely charged plates, allowing a small current to flow. If smoke enters, the radiation is absorbed by the smoke particles rather than the air molecules, and the current drops. The current drop is detected by the electronics in the device and the alarm is sounded.
The amount of radiation escaping from the smoke detector is lower than the background radiation that occurs naturally.
The amount of radiation escaping from the smoke detector is lower than the background radiation that occurs naturally.