DIY Room Intruder Alert System Using ESP32, Ultrasonic Sensor, and Telegram

Ever wanted to get a notification when someone enters your room? In this DIY project, we’ll show you how to build a smart intruder alert system using an ESP32, ultrasonic sensor, and Telegram—completely free, no third-party paid services!

🧰 Components Needed

• ESP32 Development Board (e.g., DOIT ESP32 DEVKIT V1)
• HC-SR04 Ultrasonic Sensor
• Jumper Wires
• USB Cable for ESP32
• WiFi connection
• Telegram App (for bot notifications)

🔌 Wiring Diagram

Note: While your ESP32 board might have D-labels (D1, D2, etc.), internally we use GPIO numbers in code.

📲 Telegram Bot Setup

1. Open Telegram and search for @BotFather
2. Send /start, then /newbot
3. Name your bot and assign it a username (must end in _bot)
4. Save the Bot Token provided

Get Your Chat ID

1. Open this URL in your browser (replace <TOKEN>):
   https://api.telegram.org/bot<TOKEN>/getUpdates
2. Send any message to your bot
3. Refresh the page to find your chat ID in the JSON response:
   "chat":{"id":12345678,...}

💻 Code for ESP32

#include <WiFi.h>
#include <WiFiClientSecure.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";

String botToken = "YOUR_BOT_TOKEN";
String chatID = "YOUR_CHAT_ID";

#define trigPin 5
#define echoPin 18

WiFiClientSecure client;

void setup() {
  Serial.begin(115200);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nConnected!");
  client.setInsecure();  // Skip SSL certificate validation
}

void loop() {
  long duration;
  float distance;

  // Trigger ultrasonic sensor
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;

  Serial.print("Distance: ");
  Serial.println(distance);

  if (distance < 50) {
    sendTelegramMessage("🚨 Someone just entered in your room!");
    delay(10000);  // Wait 10 sec before next message
  }

  delay(500);
}

void sendTelegramMessage(String message) {
  if (WiFi.status() == WL_CONNECTED) {
    if (client.connect("api.telegram.org", 443)) {
      String url = "/bot" + botToken + "/sendMessage?chat_id=" + chatID + "&text=" + message;
      client.print(String("GET ") + url + " HTTP/1.1\r\n" +
                   "Host: api.telegram.org\r\n" +
                   "Connection: close\r\n\r\n");
      delay(500);
    }
  }
}

🎯 How It Works

• The ultrasonic sensor continuously checks the distance in front of it.
• If the distance is less than 50 cm, it assumes someone entered the room.
• It sends a message via the Telegram Bot API directly to your Telegram app.
• There’s a 10-second cooldown to prevent spamming.

💡 Real-World Applications

• Room intrusion alert
• Baby movement detection
• Office security
• Pet activity monitoring
• Motion-triggered automation

🧪 Tips and Enhancements

• 📏 Fine-tune the distance threshold (if (distance < 50)) based on your setup
• ⏱️ Use multiple readings and averaging to reduce false alerts
• 💡 Add LED or buzzer for local alerts
• 📷 Integrate with ESP32-CAM to send photos
• 🕐 Add time-based filters (e.g., only notify at night)

output: