Parts of a Fire Alarm System – Panel, Detectors and Horns

All 11 parts on the diagram

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Start here: 5 main parts 5

Control panel The hub: it watches every device and sets off the alarm.
Smoke detector Senses the smoke particles given off by a fire.
Pull station A wall box with a handle, pulled to start the alarm.
Horn strobe Warns people with a loud sound and a flashing light.
Bell A motor-driven gong, the older kind of warning device.

The lobby: what starts an alarm 4

Annunciator A display by the entrance that shows where the alarm is.
Backup battery Runs the system when the building's power goes out.
Heat detector Responds to high temperature or a fast rise in temperature.
Waterflow switch Signals the panel when water moves in the sprinkler pipe.

The corridor: what the alarm does 2

Door holder A magnet that holds a fire door open until an alarm.
Central station A staffed center that receives the alarm and calls the fire department.

How this list was compiled: Read 2026-09-30; a name is kept only where two independent sources use it. (1) Wikipedia, Fire alarm system (its list of parts: fire alarm control panel or control unit, the hub of the system; remote annunciator, usually by the front door; secondary (backup) power supplies, batteries in the bottom of the panel or a separate box; initiating devices such as pull stations, heat detectors and smoke detectors, and a water-flow detector for the sprinklers; notification appliances such as horns, strobes and bells; magnetic smoke door holders that release a door on command from the panel), Fire alarm control panel (monitoring by a supervising or central station; sprinkler flow switches), Manual fire alarm activation and Fire alarm notification appliance. (2) A US maker's specification sheet for an addressable control panel, https://archive.org/details/manualzz-id-1215421 : fire alarm control panel, annunciator, smoke detector, heat detector, pull station, notification appliances (bells, strobes and horns), standby battery, waterflow switches, central station receivers. (3) A second US maker's service manual for a control panel, https://archive.org/details/manualzilla-id-6034733 : control panel, remote annunciator, smoke detector, pull stations, battery, doorholder points, central station. (4) A UK supplier's catalog, https://archive.org/details/manualzz-id-1221017 : control panels, smoke detectors, heat detectors, bells, batteries, door holders (it says manual call point for pull station). (5) OSHA, Fire Detection Systems, https://www.osha.gov/etools/evacuation-plans-procedures/emergency-standards/fire-detection : smoke detectors detect the visible or invisible smoke particles from combustion; heat detectors suit places where smoke detectors would give false alarms. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. A schematic, not to scale. Licence: own work

How it works

A fire alarm system is many devices wired to one cabinet. Some start an alarm, some warn people, and some act on the building. This is the kind found in offices and schools, not a single home smoke alarm.

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What starts an alarm

The control panel watches every device. A smoke detector or a heat detector on the ceiling can start an alarm by itself, a person can start one at a pull station, and a waterflow switch reports that the sprinklers are running. The annunciator by the entrance shows where the alarm is. A backup battery keeps the system going in a power cut.

What the alarm does

The panel sounds the horn strobes and bells, which the trade calls notification appliances. It lets go of each door holder, so fire doors swing shut. In most buildings it also sends a signal to a central station, where staff call the fire department.

Inputs and outputs: detectors, pull stations and switches go in; horns, bells and door holders come out.

Questions and answers

What are the main parts of a fire alarm system?

A control panel with a backup battery; initiating devices, which are smoke detectors, heat detectors, pull stations and waterflow switches; notification appliances, which are horns, strobes and bells; and often an annunciator, door holders and a link to a central station.

What is the difference between a smoke detector and a heat detector?

A smoke detector senses the particles a fire gives off. A heat detector responds to temperature. Heat detectors are used where smoke detectors would give false alarms, such as kitchens, furnace rooms and garages.

What is a pull station?

A wall box with a handle, usually near an exit, that a person pulls to start the alarm by hand. Outside North America the same device is called a manual call point, and many are worked by pressing a panel instead.

What does an annunciator do?

It repeats what the control panel knows on a small display somewhere more useful, usually by the front door. Firefighters arriving at the building read it to see which device or area is in alarm.

What is the difference between a fire alarm system and a smoke alarm?

A smoke alarm is one unit with its own sensor and horn, the kind fitted in homes. A fire alarm system joins many separate detectors and warning devices to one control panel, so that any of them can set off all the others.