Eighty percent of all smoke detectors in the home utilize americium-241. This radioactive element possesses a half life of 432 years, according to the EPA.
When oxygen and nitrogen impact the device, electrons from the molecules are knocked off by americium-241. As this occurs, a positive ion is created, which attaches to a negatively-charged metal plate during normal use.
If smoke is absorbed into the detector, the process of ionizing the molecules cannot occur. When the ions do not impact the negatively-charged plate, the device is set off.
Without the americium-241, smoke detectors would not be able to function.
Americium-241 releases only alpha radiation, which, according to the EPA, causes very little environmental impact in the form of radioactivity. Most importantly, smoke detectors in the U.S. use plastic casing to block the element.