Three main types of smoke detectors:

– Ionization: Installed in an estimated 90 percent of American homes, they use the radioactive element americum-241 to set up an electrical current between two metal plates. When smoke interrupts the current, the alarm sounds. Ionization detectors work best in open, flaming fires.

– Photoelectric smoke detectors have an internal beam of light that is deflected by smoke particals, triggering the alarm. They work better – meaning sooner – in smoldering, smokey fires.

– Combination detectors have both types of sensor, ionization and photoelectric.

AP-ES-02-09-08 1251EST