Fire Alarm Devices

The Full Picture

The devices fall into two groups. Initiating devices send a signal to the panel: smoke detectors, heat detectors, manual pull stations, duct detectors and monitor modules that report on items such as sprinkler waterflow and valve tamper switches. Notification appliances receive a signal from the panel and warn occupants: horns, strobes, combination horn/strobes and speakers. NFPA's fire alarm basics fact sheet describes the circuits that connect the panel to each of these groups.

Devices appear as symbols on the fire alarm floor plans, with a legend that defines each symbol and often a device schedule or matrix of what each one does. Candela ratings of strobes and the type of detector are noted on the legend or the plan. The riser diagram shows the panel, annunciator and any remote power supplies. Specs name approved device types and the manufacturer family, which matters because devices on an addressable system must be compatible with the panel.

The takeoff unit is EA, sorted by type and, for appliances, by variant such as wall or ceiling mount and strobe rating. Add-on items count too: back boxes, mounting plates, addressable modules, end-of-line resistors where used, and detector bases. Cable and raceway are separate lines. Counting is done by symbol on each floor plan, with a check against the legend and any device count the drawings provide, since a missed floor or room is the most common error.

Typical pitfalls are mixing up combination devices with separate horns and strobes, leaving out duct detectors and modules that are shown only on the mechanical or sprinkler drawings, and missing devices in spaces such as elevator machine rooms and stairs. Coordination matters: the sprinkler contractor often supplies waterflow and tamper switches that the fire alarm contractor connects, so scope and counts must agree.