Home Safety Alert: MQ-2 Gas & Smoke Detector with Buzzer & Arduino

Liquefied petroleum gas (LPG) and combustible gas leaks in home kitchens or 3D printer enclosures pose severe safety hazards. The MQ-2 electrochemical gas sensor utilizes a tin-dioxide (SnO2) sensitive layer whose electrical conductivity increases in the presence of combustible hydrocarbons and smoke particles.

1. Pin Connections

• MQ-2 VCC → Arduino 5V
• MQ-2 GND → Arduino GND
• MQ-2 AOUT → Arduino Analog A0
• Buzzer (+) → Arduino Digital Pin 8
• LED Anode → Arduino Digital Pin 9 (via 220Ω resistor)

2. Arduino Code

cpp
const int GAS_PIN = A0;
const int BUZZER_PIN = 8;
const int LED_PIN = 9;
const int ALARM_THRESHOLD = 300;

void setup() {
  Serial.begin(9600);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  Serial.println("MQ-2 Preheating (approx 20 seconds)...");
}

void loop() {
  int gasLevel = analogRead(GAS_PIN);
  Serial.print("Current Gas Level: ");
  Serial.println(gasLevel);

  if (gasLevel > ALARM_THRESHOLD) {
    digitalWrite(LED_PIN, HIGH);
    tone(BUZZER_PIN, 1000); // 1KHz alarm tone
  } else {
    digitalWrite(LED_PIN, LOW);
    noTone(BUZZER_PIN);
  }
  delay(300);
}