How Do Photoelectric Smoke Detectors Work?
All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120-volt house current. Inside Photoelectric smoke detectors there is a light and a sensor, but they are positioned at 90-degree angles to one another, like this: In the normal case, the light from the light source on the left shoots straight across and misses the sensor. When smoke enters the detection chamber of the smoke detector, the smoke particles scatter the light and some amount of light hits the sensor. The sensor then sets off the horn in the smoke detector. Photoelectric detectors are better at sensing smoky fires, such as a smoldering mattress.
