Photoelectric Smoke Alarms
A photoelectric (optical) smoke alarm “sees” the smoke. Photoelectric (optical) smoke alarms operate
on the principle of light scattered from the surface of particles.
Smoke entering the sensing chamber reflects light onto the sensor, which triggers the alarm. Because
large particles have much more surface area than small particles, a photoelectric smoke alarm is more
sensitive to the large smoke particles produced in a smoldering fire such a foam filled furnishing.
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In the normal case, the light from the light source shoots straight across and misses the sensor. When
smoke enters the chamber, however, the smoke particles scatter the light and some amount of light hits
the sensor, activating the alarm.
Advantages:

Good for smoldering fires and dense smoke

Not as prone to cooking nuisance alarms

Contain no radioactive material

Suitable for general use
Disadvantages:

Prone to nuisance alarms from dust and insects – must be kept clean

More expensive