A smoke detector is a system that alerts building residents to the existence of a fire until it spreads quickly and prevents escape or efforts to evacuate it. When smoke detectors sense it, they emit a loud, high-pitched warning sound that is normally warbling or sporadic, and followed by a flashing light. Photoelectric and ionization smoke detectors are the two types available. A light-sensitive cell is used in one of two ways in photoelectric smoke detectors. The other photoelectric sensor, which is commonly used in private residences, uses a detection chamber that is formed in such a way that the light-sensitive device cannot normally “see” the light source.