The F220 Photoelectric Smoke Detectors are UL Listed, open-area photoelectric smoke detectors. Use them with commercial fire protective signaling systems and household fire warning systems (see NFPA 72, the National Fire Alarm Code). These smoke detectors scatter light using a pulsed infrared source operating with a gated, high-speed, photodiode infrared sensor. The symmetry of the optical chamber allows 360° uniform smoke entry, but minimizes external light entry. The detectors use low current electronic circuitry, so they can connect to 12 VDC nominal or 24 VDC nominal power source circuits.