Smoke Detector

Smoke detectors are used in public places, offices or factory buildings for fire detection. The commonly used smoke detectors are of the ionizing type and utilize a low-level radioactive source of americium-241. Americium-241 emits alpha particles which ionize the air in the detector, i.e. atoms in air dissociate into electrically charged ions and electrons, forming an electric current flowing through two electrodes in the detector. When a fire occurs, the smoke entering the detector will block the ions and cause a sudden drop in the electric current, thus triggering the alarm. Since the radioactivity of americium-241 in the smoke detector is extremely low, and alpha particles are easily blocked outside the detector because of their very weak penetrating power, properly installed smoke detectors will not affect people's health.