Introduction

A Fire Alarm Circuit is a safety system designed to detect fire or high temperature and alert people by triggering an alarm. Fire alarms play a crucial role in preventing loss of life and property by providing early warnings during fire accidents.

This project demonstrates how electronic sensors can be used to detect fire and activate an alarm automatically.

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Objective of the Project

The main objectives of this project are:

• To detect fire or excessive heat at an early stage.
• To alert people using a buzzer or alarm.
• To understand the working of fire/temperature sensors.
• To design a simple and reliable safety system.

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Working Principle

The fire alarm works based on temperature or flame detection.

Method 1: Using Flame Sensor / Thermistor

• A flame sensor or thermistor detects the presence of fire or abnormal heat.
• When fire is detected, the sensor output changes.
• This signal activates a transistor or relay.
• The buzzer or alarm turns ON immediately.

Method 2: Using Arduino (Smart Fire Alarm)

• Arduino continuously monitors the sensor value.
• When the value crosses a preset threshold, Arduino triggers a buzzer and LED.
• The threshold can be adjusted through software.

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Components Required

Basic Fire Alarm Circuit

• Flame sensor or Thermistor
• Transistor (BC547)
• Buzzer
• Resistors (10kΩ, 220Ω)
• Power Supply (5V–12V)
• Breadboard & wires

Arduino-Based Fire Alarm

• Arduino Uno
• Flame Sensor / LM35 Temperature Sensor
• Buzzer
• LED
• Resistors
• Jumper wires

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Circuit Diagram

Basic Fire Alarm Circuit

Sensor Output ---- 10kΩ ---- Base of Transistor (BC547)

Collector ---- Buzzer ---- +Vcc
Emitter ------------------ GND

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Arduino-Based Circuit

Flame Sensor OUT ---- Arduino A0
Buzzer ------------- Arduino D8
LED ---------------- Arduino D9
VCC ---------------- 5V
GND ---------------- GND

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Arduino Code for Fire Alarm Circuit

int flameSensor = A0;
int buzzer = 8;
int led = 9;
int threshold = 300;

void setup() {
  pinMode(buzzer, OUTPUT);
  pinMode(led, OUTPUT);
}

void loop() {
  int sensorValue = analogRead(flameSensor);

  if (sensorValue < threshold) {
    digitalWrite(buzzer, HIGH);
    digitalWrite(led, HIGH);
  } else {
    digitalWrite(buzzer, LOW);
    digitalWrite(led, LOW);
  }
}

Code Explanation

• Arduino reads sensor data continuously.
• If fire is detected (value below threshold), alarm activates.
• LED provides visual indication along with sound alert.

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Advantages

• Fast response time
• Simple and cost-effective
• Improves safety
• Easy to install
• Can be expanded with IoT features

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Applications

• Homes and apartments
• Offices and factories
• Schools and colleges
• Warehouses
• Industrial safety systems

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