Smart Safety: Monitoring Fire and Gas with ESP32

In the world of DIY electronics, few projects are as practical and rewarding as a home safety monitor. Whether it's a gas leak in the kitchen or an unexpected temperature spike, early detection saves lives.

Today, we are diving into a project that uses the ESP32 to monitor environmental hazards and send real-time alerts directly to your phone via Telegram.

🛠 Hardware Components

To build this system, you'll need the following hardware:

ESP32 Microcontroller - The "brain" with built-in Wi-Fi.
MQ-2 Gas Sensor - Detects smoke, LPG, and flammable gases.
Flame/Fire Sensor - Detects IR light emitted by fire.
DHT11 Sensor - Measures ambient temperature and humidity.
Relay Module - Controls a high-voltage device (like a water pump).
Buzzer & LEDs - Local visual and audible alarms.

💻 Software & Libraries

The system is written in C++ using the Arduino IDE framework. To compile the code, you'll need to install these libraries:

WiFi.h: Handles the connection to your local internet.
HTTPClient.h: Used to make requests to the Telegram API.
DHT.h: Specifically designed to interface with the DHT11/22 temperature sensors.

⚙️ How It Works: The Logic

The system operates on a continuous loop, checking three main environmental factors:

1. Gas/Smoke Detection

The MQ-2 sensor provides an analog value. If the value exceeds 330 (the defined threshold), the blue LED lights up, the buzzer sounds, and a Telegram notification is sent.

2. Temperature Monitoring

The DHT11 tracks the room temperature. If it crosses 35.0°C, the yellow LED warns the user of potential overheating.

3. Fire Response & Mitigation

This is the most critical part. When the Flame Sensor detects fire (indicated by a LOW state):

A Red LED and the Buzzer turn on immediately.
The Relay triggers a water pump to extinguish the fire.
An emergency Telegram alert is dispatched.

📜 The Complete Code

Below is the implementation. Make sure to replace ssid, password, Bot token, and chatId with your actual credentials.

#include <WiFi.h>
#include <HTTPClient.h>
#include "DHT.h"

// === PIN CONFIGURATION ===
#define MQ2_PIN          34  // Gas sensor analog
#define FIRE_SENSOR_PIN  35  // Fire sensor digital
#define LEDRED_PIN       18
#define LEDBLUE_PIN      2
#define LEDGREEN_PIN     4
#define LEDYELLOW_PIN    23
#define BUZZER_PIN       27
#define DHTPIN           33
#define DHTTYPE          DHT11
#define RELAY_PIN        14  // Relay controlling water pump

DHT dht(DHTPIN, DHTTYPE);

// === THRESHOLDS ===
#define GAS_THRESHOLD    330
#define TEMP_THRESHOLD   35.0

// === WiFi & Telegram Info ===
const char* ssid = "your_SSID";
const char* password = "your_PASSWORD";
String BOT_TOKEN = "your_BOT_TOKEN";
String CHAT_ID = "your_CHAT_ID";

// === State Management Flags ===
bool gasAlertSent = false;
bool tempAlertSent = false;
bool fireAlertSent = false;

void connectWiFi() {
  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\n✅ WiFi connected!");
}

void sendTelegramAlert(String msg) {
  if (WiFi.status() == WL_CONNECTED) {
    HTTPClient http;
    // Constructing the Telegram Bot API URL
    String url = "https://api.telegram.org/bot" + BOT_TOKEN + "/sendMessage?chat_id=" + CHAT_ID + "&text=" + msg;
    http.begin(url);
    int httpCode = http.GET();
    if (httpCode > 0) Serial.println("✅ Telegram alert sent!");
    else Serial.println("❌ Error sending Telegram message.");
    http.end();
  }
}

void setup() {
  Serial.begin(115200);
  delay(2000);
  dht.begin();
  connectWiFi();
  analogReadResolution(10); // Standardize analog range

  pinMode(MQ2_PIN, INPUT);
  pinMode(FIRE_SENSOR_PIN, INPUT);
  pinMode(LEDRED_PIN, OUTPUT);
  pinMode(LEDBLUE_PIN, OUTPUT);
  pinMode(LEDGREEN_PIN, OUTPUT);
  pinMode(LEDYELLOW_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  pinMode(RELAY_PIN, OUTPUT);

  // Initial State: Safe Mode
  digitalWrite(LEDRED_PIN, LOW);
  digitalWrite(LEDBLUE_PIN, LOW);
  digitalWrite(LEDGREEN_PIN, HIGH); // Green ON means everything is OK
  digitalWrite(LEDYELLOW_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);
  digitalWrite(RELAY_PIN, HIGH);    // Relay is usually Active LOW, so HIGH = OFF
}

void loop() {
  int gasValue = analogRead(MQ2_PIN);
  int fireState = digitalRead(FIRE_SENSOR_PIN);
  float temp = dht.readTemperature();

  // Basic Error Handling for Sensor
  if (isnan(temp)) {
    Serial.println("❌ Failed to read from DHT sensor!");
    temp = 0;
  }

  // --- 1. GAS DETECTION LOGIC ---
  if (gasValue > GAS_THRESHOLD) {
    digitalWrite(LEDBLUE_PIN, HIGH);
    digitalWrite(LEDGREEN_PIN, LOW);
    digitalWrite(BUZZER_PIN, HIGH);
    if (!gasAlertSent) {
      sendTelegramAlert("🚨 Gas/Smoke Detected! Value: " + String(gasValue));
      gasAlertSent = true;
    }
  } else {
    gasAlertSent = false;
    digitalWrite(LEDBLUE_PIN, LOW);
  }

  // --- 2. TEMPERATURE LOGIC ---
  if (temp >= TEMP_THRESHOLD) {
    digitalWrite(LEDYELLOW_PIN, HIGH);
    if (!tempAlertSent) {
      sendTelegramAlert("🌡️ High Temp! Temp: " + String(temp) + "°C");
      tempAlertSent = true;
    }
  } else {
    tempAlertSent = false;
    digitalWrite(LEDYELLOW_PIN, LOW);
  }

  // --- 3. FIRE DETECTION LOGIC ---
  if (fireState == LOW) { 
    digitalWrite(LEDRED_PIN, HIGH);
    digitalWrite(BUZZER_PIN, HIGH);
    digitalWrite(RELAY_PIN, LOW); // Trigger Pump
    if (!fireAlertSent) {
      sendTelegramAlert("🔥 FIRE DETECTED! Water Pump Activated!");
      fireAlertSent = true;
    }
  } else {
    fireAlertSent = false;
    digitalWrite(LEDRED_PIN, LOW);
    digitalWrite(RELAY_PIN, HIGH); // Pump OFF
  }

  // Master Green LED Control
  if (gasValue <= GAS_THRESHOLD && temp < TEMP_THRESHOLD && fireState != LOW) {
    digitalWrite(LEDGREEN_PIN, HIGH);
    digitalWrite(BUZZER_PIN, LOW);
  } else {
    digitalWrite(LEDGREEN_PIN, LOW);
  }

  delay(1000); 
}

🚀 Key Takeaways

State Management: Notice the use of gasAlertSent flags. This prevents the ESP32 from spamming your Telegram account with 1,000 messages a minute once a threshold is hit.
Safety First: The code defaults the Green LED to ON only when all conditions are safe, providing an instant visual confirmation of system health.
Scalability: You could easily add a Blynk or Home Assistant integration to this setup for a full dashboard view.