Since a common point or zone is used to identify the circuit in alarm, exact locations are left to field investigation. Addressable fire alarm systems allow multiple device types to be installed on the same circuit without the need for specific zones to be grouped with circuits. Since each device is individually addressed, smoke detectors, manual fire alarm stations or other types of devices can be wired on the same circuit, but still allow specific information on the type of device in alarm and its location. Heat detectors sense the surrounding temperature of a room to determine if a rise in temperature occurs. Since fire produces heat, a rise in temperature can mean a fire is present.
Heat detectors use either a fixed temperature level or a rise in temperature to produce an alarm.
Ionization detectors use an electrical grid within the detector to sense a fire. When particles from a fire pass through the grid, the electrical characteristics change and cause an alarm to be produced by the detector. Ionization detectors are useful when trying to sense a hotter fire that produces smaller particles of combustion. Photoelectric detectors use a light beam within the detector to sense a fire. When particles enter the detector's chamber, the light beam is obscured.