Alarm

 An alarm panel is the system's "brain," receiving signals from detectors, activating alarms, and often monitoring power and communication. Heat detectors work by activating at a preset fixed temperature or when a rapid temperature increase occurs. Smoke detectors use either a small radioactive source to detect changes in electrical current (ionization type) or a light beam that is scattered or absorbed by smoke (photoelectric type) to trigger an alarm.  

This video explains the basics of how heat detectors work:

Alarm Panel

Function: Receives signals from fire detectors, sounds the alarm (horns, sirens, strobe lights), and may alert a monitoring service or emergency responders. 

Components: Contains the central control unit and a battery backup for power outages. 

Communication: Connected to initiating devices (detectors) through wiring that monitors their status, usually by zone. 

Heat Detectors

Purpose: Detect fire by sensing temperature changes in the surrounding environment. 

Types of Activation:

Fixed-Temperature: Activates when the temperature reaches a specific, predetermined threshold. 

Rate-of-Rise: Activates when the temperature rises rapidly, indicating a fast-developing fire. 

Activation Mechanisms: Can use bi-metal strips that bend with heat to close a circuit, or a thermistor whose resistance changes with temperature to send a signal to the control panel. 

Smoke Detectors

Purpose: Detect smoke particles in the air, a primary symptom of a fire. 

Types and Principles:

Ionization: A small, safely shielded radioactive source ionizes the air in a chamber, creating a small electric current. When smoke particles enter, they attach to ions, reducing the current and triggering the alarm. 

Photoelectric: Uses a light source and a photocell. In the absence of smoke, the light beam does not hit the cell. When smoke enters the chamber, the light is scattered or refracted onto the photocell, triggering the alarm. 

Advantages: Generally provide a faster response than heat detectors, but can also be prone to false alarms. 

System Operation

When a fire occurs, a smoke or heat detector senses the smoke or temperature. It sends an alarm signal to the fire alarm control panel. The panel then activates notification devices, such as sirens and lights, to alert people to evacuate

 and call for help.