What type of smoke detector uses a small amount of radioactive material in the sensing chamber?

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Ionization smoke detectors use a tiny amount of radioactive material in the sensing chamber. The radioactive source ionizes the air inside, creating a small current between two electrodes. When smoke enters the chamber, the smoke particles attach to the ions and reduce the current, triggering the alarm. This design makes them especially quick to detect flaming fires that produce small combustion particles. The other common type, photoelectric detectors, rely on light—either a light beam that gets blocked by smoke (obscuration) or light that is scattered toward a sensor by smoke particles—and do not use radioactive material.