Fire alarm control panel – After signals come in from detectors, the FACU will send signals to the outputs, the notification devices, to alert people in the vicinity. Recalling elevators, notifying any monitor station, and turning off the HVAC system are also functions of the FACU. Devices to initiate – Devices come in the form of pull stations and detectors for duct, smoke, beam, and heat. Tamper switches and flow switches are also initiating devices. Pull stations – These alarm stations are the conventional hand-operated fire alarm initiators we all see along walls. They are red and white in color, making them stand out and universally recognizable. Duct detectors – Installed within AC and heating ducts, these recognize when smoke is in the duct, and turn off air handling units to prevent smoke from spreading throughout the facility by ducts. Smoke detectors – Senses smoke, and they have two classifications. Ionization detectors signal when smoke particles disrupt ions flowing between two electrically charged plates. Photoelectric detectors have a small chamber where LED lights shoot a beam and signal when smoke particles scatter the beam of light within the small chamber. Heat detectors – Two methods comprise heat detectors, Rate-of-rise, and fixed temperature. The rate-of-rise detector will signal if the rate at which the temperature rises is higher than a specific value. Fixed temperature signals when the element is at or above the specified value. Aspirating/air sampling smoke detector – The air sampling method uses tubes for air/smoke to travel to a central detector to recognize minuscule changes to the chemical composition of the sample air. Flow switches – Using paddles within water-filled pipes, water flow switches are designed to work if water flows from a single sprinkler. Devices for notification – Used as the notification system for audio and visual notification to occupants. Tamper switches – Initiating device that signals if the valve is moved from the regular position. Sound devices – Sirens, bells, and horns designed to notify occupants audibly. Strobes – Lights designed to flash as a visual notifier. Dialers/Communicators – Certain alarm systems are equipped with internal or external dialers to contact monitoring centers or receiving stations. They may use radio signals, internet, or phone lines to establish the signal. Notification Appliance Circuit (NAC) Power Supply – With the advanced fire protection systems developed for today, extra power is required. This is where the NAC Power Supply comes into play to ensure the notification systems, switches, detectors, etc. are all operable in time of need.