Fire Alarm Systems Basics

Basics on Components, power, and signaling

Initiating Devices

Detect fire-related conditions and send signals to the FACU.

Smoke Detectors

Ionization, Photoelectric, and Beam

Manual Pull Stations

Devices that allow individuals to manually trigger the fire alarm.

Waterflow and Pressure Switches

Devices that monitor water flow and pressure in fire protection systems.

IDC (initiating Devices Circuit)

Used in conventional systems

SLC (Signaling Line Circuit)

Used in addressable systems for more precise monitoring

Primary Power

Typically from utility or generator

Secondary Power

Batteries or SEPSS (Stored-Energy Emergency Power Supply System)

Battery Sizing 

Must support 24 hours standby + 5-15 minutes alarm time.

Audible & Visual Alerts

Speakers, horns, strobes—activated via Notification Appliance Circuits (NACs).

Public Mode

Alerts all occupants.

Private Mode

Alerts only responders (e.g., hospital staff).

Temporal Patterns

Temporal 3 for fire evacuation; Temporal 4 for carbon monoxide.

Relays & Control Circuits

Used to operate systems like elevator recall/shutdown, fire door closers, and smoke control systems.

Supervising Stations

Fire alarms can send signals to external monitoring centers.

Public Emergency Alarm Reporting Systems (PEARS)

Systems used for off-premises signaling

Central, Proprietary, or Remote Supervising Stations

Types of external monitoring centers for fire alarms.

Fire Alarm Control Unit (FACU)

The central unit that monitors inputs (Detectors) and controls outputs (Alarms, emergency systems).

Heat detectors

Fixed, rate-of-rise, and analog

Carbon monoxide detectors

Devices that detect the presence of carbon monoxide.

Alarm (Example: Smoke)

Immediate threat detected

Trouble (Example: Broken wire)

Fault in the system

Supervisory (Example: Closed Sprinkler Valve)

Issue with monitored equipment

P.E.A.R.S.

Public Emergency Alarm Reporting Systems

Temporal 3

Fire Evacuation

Temporal 4

Carbon Monoxide

N.A.C.

Notification Appliance Circuits