Which smoke alarm/detector is activated by the visible products of combustion?

• A. Photoelectric
• B. Ionization
• C. Heat
• D. Carbon Monoxide detector

Answer: (A)

Photoelectric smoke alarms are activated by visible smoke because they detect smoke through light scattering. Inside the unit, a light beam runs across a chamber and a sensor watches for scattered light. When smoke particles from combustion enter the chamber, they scatter the light toward the sensor, triggering the alarm. This makes them especially responsive to smoldering fires that produce substantial visible smoke. Other detectors work differently: ionization detectors use a small radioactive source to ionize air and respond best to the tiny particles from flaming fires; heat detectors respond to high temperatures, not smoke; carbon monoxide detectors sense CO gas, not smoke. So the detector that fires in response to visible products of combustion is the photoelectric one.