Which statement describes how a photoelectric smoke detector generates a warning?

• A. A fiber-optic beam that is interrupted by smoke.
• B. Smoke particles refract light in the detector unit causing the photoelectric cell to conduct electricity and trigger the alarm.
• C. Smoke blocks a laser beam in a laser-based smoke detector.
• D. The detector measures gas conductivity changes with smoke.

Answer: (B)

Photoelectric smoke detectors detect smoke by using a light source and a photosensitive sensor inside a chamber. In clean air, the light does not reach the sensor. When smoke enters, the smoke particles scatter the light, and some of that scattered light reaches the photosensitive element. The sensor then produces an electrical signal that trips the alarm. This is the mechanism described in the statement: smoke causes light to interact with the detector’s light-sensing element, triggering a warning. The other options describe different technologies—fiber-optic beam detectors rely on the beam being interrupted, laser-based detectors rely on blocking a laser beam, and gas-conductivity changes are not how a photoelectric detector operates.