Most household smoke detectors – known as “ion chamber” detectors – contain a very small amount of Americium-241, a radioisotope that is artificially created by bombarding plutonium with neutrons.

The material was discovered during the Manhattan Project, and was first offered to industry in the early 1960s. The majority of Americium produced goes into making smoke detectors. One gram of the material is enough to equip some 5,000 detectors.

How does it work? Basically, the Americium emits alpha particles of radiation, which create ions of oxygen and nitrogen in the detector. A small electrical charge (supplied by DC or AC power) usually catches these ions. But when smoke enters the detector, it absorbs the alpha particles, the ionization rate falls, and the electrical current dips, causing the alarm goes off.

Is the degree of radiation dangerous to people or pets? Not hardly. A smoke detector puts out negligible dose (far less than the background radiation you’re exposed to constantly). And don’t worry about disposing of a smoke detector, either. They’re perfectly safe to add to your regular household garbage. Just make sure you remove the battery and dispose of it properly.