Ionization smoke alarms use a small amount of radioactive material to ionize air between two electrical contacts in a small detection chamber (National Fire Protection Association, 2015). The ionized air allows electrical current to flow between the two contacts, completing a circuit. When smoke particles enter the detection chamber they break the circuit, which results in the alarm tripping.
The most common radioactive material used for ionization type smoke alarms, Americium-241, has a half-life of approximately 432 years, several times the recommended 10 year product life (Environmental Protection Agency 2015). Furthermore, the amount of Americium-241 present in the smoke alarm and its process of decay ensure that consumers are exposed to negligible amounts of radiation (World Nuclear Association 2014).