Fire Detection & Alarm System

Skills & Concepts You'll Gain

How a flame sensor detects infrared light from fire
How to use digital and analog sensor readings together
How to trigger buzzer alarms for safety systems
How to build real-world safety and alert systems
Foundation for home security, industrial safety, and IoT projects

Tech Used: Arduino UNO, Flame Sensor Module, Active Buzzer, Red LED, Arduino IDE

Step 1

Understand the Flame Sensor

The flame sensor detects infrared (IR) light that fire produces. It has a small IR receiver that is sensitive to the wavelength of fire light.

The module has 3 pins:

VCC → 5V on Arduino
GND → GND on Arduino
DO (Digital Output) → Pin 7 on Arduino - gives LOW when fire is detected, HIGH when no fire

The flame sensor output is inverted - it gives LOW (0) when fire IS detected and HIGH (1) when there is NO fire. Keep this in mind when writing the code!

Step 2

Wire the Circuit

Flame Sensor: VCC → 5V, GND → GND, DO → Pin 7
Red LED: Positive leg → Pin 6 (via 220Ω resistor), Negative leg → GND
Buzzer: Positive (+) → Pin 8, Negative (-) → GND

Wiring Diagram

Keep the flame sensor away from direct sunlight and strong light sources, as they can cause false fire detection due to infrared interference.

Step 3

Write the Code by opening Arduino UNO

fire_detection.ino

// Fire Detection & Alarm - NKDevSpace Tutorial

const int flameSensor = 7;
const int redLED      = 6;
const int buzzerPin   = 8;

void setup() {
  pinMode(flameSensor, INPUT);
  pinMode(redLED, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
  Serial.begin(9600);
  Serial.println("Fire Detection System Ready!");
}

void loop() {
  int flameStatus = digitalRead(flameSensor);

  // Flame sensor gives LOW when fire is detected
  if (flameStatus == LOW) {
    Serial.println("🔥 FIRE DETECTED! ALARM ON!");
    digitalWrite(redLED, HIGH);   // Red LED ON
    tone(buzzerPin, 2000);        // Buzzer alarm at 2000 Hz
  } else {
    Serial.println("✅ No fire. All safe.");
    digitalWrite(redLED, LOW);    // Red LED OFF
    noTone(buzzerPin);            // Buzzer OFF
  }

  delay(500);  // Check every 0.5 seconds
}

Step 4

Code Explanation

digitalRead(flameSensor)

Reads the flame sensor pin. It returns either 0 (LOW) or 1 (HIGH). Since the sensor is inverted, LOW means fire detected.

if (flameStatus == LOW)

This checks if fire is detected. Remember - the sensor gives LOW when it sees fire. So we check for LOW, not HIGH. This is the inverted logic of the sensor.

tone(buzzerPin, 2000)

Activates the buzzer at 2000 Hz - a high-pitched alarm sound. You can change the frequency to make it sound different. noTone() silences it.

delay(500)

The system checks for fire every 500 milliseconds (0.5 seconds). This is fast enough to detect fire quickly without overloading the Arduino.

Step 5

Test the Project

Make sure your Arduino Uno is connected to your laptop using a USB cable
If not already selected, choose the correct settings:
- Go to Tools → Board → Arduino AVR Boards → Arduino Uno
- Go to Tools → Port → COM X(COM 3, COM4, ...) (Arduino Uno)
Open Tools → Serial Monitor
Set the baud rate to 9600
You should see the message "No fire. All safe." repeating every 0.5 seconds
Check that the LED is OFF and the buzzer is silent in normal condition
Now carefully bring a lit candle or lighter near the flame sensor (keep safe distance)
When fire is detected:
- Red LED turns ON
- Buzzer starts making sound
- Serial Monitor shows Fire detected
Move the flame away from the sensor
The system should return to normal:
- LED turns OFF
- Buzzer stops
- Message changes back to "No fire. All safe."

Safety first! Keep the flame at least 10-15 cm away and never leave it unattended.

Step 6

Try It Yourself - Challenges

Make the buzzer beep in a pattern (ON 200ms, OFF 200ms) instead of continuous sound
Add a green LED that stays ON when there is no fire (safe indicator)
Add a smoke sensor (MQ-2) alongside the flame sensor for better detection
Send an alert message via GSM module to a phone number when fire is detected

Components Needed