A fire alarm system is number of devices working together to detect and alert people through visual and audio appliances when smoke/fire is present. These alarms may be activated from smoke detectors, and heat detectors. An addressable fire alarm system is made up of a series of fire detectors and devices that are connected back to a central control panel. With addressable systems, each device has an address or location, enabling the exact detector that was triggered to be quickly identified.
How they work: Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm. A special module is installed into a fire alarm panel that is supervised by the receiving equipment for “line fault”, “common trouble”, “supervisory” and “alarm“. NAC: Short for “Notification Appliance Circuit”. Also called the Bell Circuit, Signal Circuit, or Output Circuit.