Answer: Americium

Synthetic chemical elements, elements that don’t naturally occur outside of a laboratory and must be created artificially, are few and far between. Not only are they typically unstable once created, but they are generally of little use outside of exotic laboratory experiments. In fact, of the 24 synthetic elements like Rutherfordium, Hassium, and Ununtrium, there’s only one synthetic element that has proven itself practical for household use: Americium.

Americium is a relatively soft radioactive metal, first synthesized in 1944 as part of the Manhattan Project’s research. Among the uses that have been found for the metal, such as using it in neutron sources for research or as part of specialty spectrometers, it has found a much more widespread use in the home.

Across the world, millions of people have Americium (in the form of Americium Dioxide) hard at work in their smoke detectors. Ionization-type smoke detection, one of the most common technologies used in home smoke detectors, relies on a source material to emit alpha particles to detect smoke particles. Americium is particularly well suited for the task and a tiny amount is found in nearly every ionization-type smoke detector.