What triggers a photoelectric smoke detector to initiate an alarm?

A photoelectric smoke detector operates based on the principle of light scattering. It contains a light source, typically an infrared LED, and a light-sensitive sensor. When smoke enters the detection chamber, the particles in the smoke scatter the light emitted by the LED. This scattering causes a portion of the light to be redirected towards the sensor, triggering the detector to initiate an alarm.

This mechanism is distinct from the operation of other types of smoke detectors. For example, heat from flames typically activates heat detectors or ionization smoke detectors, which utilize different principles, such as changes in ionization levels or temperature drops. Therefore, in the context of smoke detection, it is the visible smoke particles obscuring the light source that is the correct trigger for a photoelectric smoke detector to activate an alarm.