Final answer:
Ionization smoke detectors, containing americium-241, detect smoke by its interference with ion flow in the chamber, triggering an alarm. They are one of the most common smoke detectors and are safe unless tampered with.
Step-by-step explanation:
The three most common types of smoke detectors are ionization, photoelectric, and combination units. Ionization smoke detectors, which contain americium-241, use a-decay to ionize the air in an ionization chamber. As a result, a small electric current flows between two electrode plates.
When smoke enters, it impedes the ion flow, which in turn reduces the current and triggers an alarm. The americium, although radioactive, is safely contained within the device and poses no harm unless the chamber is dismantled. It's important to note that the battery in these detectors requires regular replacement due to the constant current drain.