How does a smoke alarm work?

Smoke reflects light that can be measured. Within the smoke alarm is the so-called "smoke chamber". This chamber contains an infrared diode that permanently emits light signals. These signals don't come into contact with the light-sensitive photoelectric cells until smoke particles enter the chamber.

If, however, smoke particles spread to the smoke alarm's measuring chamber during a fire, this light is reflected by the infrared diode in such a manner that the light impulses hit the highly sensitive photo element. This effect is interpreted by the following electronic system as a fire hazard and the smoke detector immediately sounds an alarm.