The smoke sensor is a T-shaped chamber with an infrared LED placed in the left opening that emits a beam of light across the horizontal portion of the chamber. The right opening is open for smoke particles to enter as base opening for the phototransistor. The phototransistor generates a current when exposed to light. If there is no smoke present inside the chamber, the beam of light is emitted across the top of the T-shaped chamber. Thus, the phototransistor does not generate current as no light has hit it. When smoke particle enter the T-shaped chamber, however the beam of light is scattered by smoke particles. Subsequently, some of the light is directed down into the vertical portion of the T-shaped chamber and strikes the phototransistor.