Build a Wi-Fi SMS Alert System with XIAO ESP32 & Sensor

Learn how to create a real-time Send SMS Alert using Seeed Studio XIAO ESP32, an ultrasonic sensor, and a free cloud API — no GSM module needed!

📲 Intro: Real-Time SMS Alerts with IoT Magic

Have you ever wanted your IoT device to send text alerts instantly without relying on bulky GSM hardware? This project shows how to build a compact SMS alert system using the ultra-small Seeed Studio XIAO ESP32-S3 development board and a simple ultrasonic sensor. The project uses Wi-Fi and a free cloud API to deliver SMS messages, making it perfect for home monitoring, security alerts, or remote systems automation. This setup is beginner-friendly and doesn’t require a GSM shield or SIM card — just Wi-Fi and a bit of Arduino code.

🔧 What You’ll Build

You’ll create a system that:

• Continuously measures distance using an HC-SR04 ultrasonic sensor.

• Detects motion or proximity within a set threshold.

• Sends an SMS notification over Wi-Fi using a cloud API when motion is detected.

• Shows real-time status via the Serial Monitor.

🔄 How It Works: System Workflow

1. Boot & Wi-Fi Setup — The XIAO ESP32 connects to your Wi-Fi network.

2. Distance Monitoring — The HC-SR04 continuously measures proximity.

3. Threshold Detection — When an object moves closer than your threshold (e.g., 100 cm), the system flags motion.

4. SMS Trigger — The ESP32 makes an HTTP POST request to the cloud API with alert details.

5. SMS Delivery — The cloud API formats & sends your text message to your phone.

💡 All communication happens over Wi-Fi — no GSM module or SIM card required!

🧠 Why Use Seeed XIAO ESP32-S3?

The Seeed XIAO ESP32-S3 stands out because it’s:

• Extremely compact, ideal for tight spaces.

• Wi-Fi & Bluetooth capable, ready for IoT projects.

• Arduino IDE compatible, so it’s perfect for beginners.

• Cost-effective compared to larger ESP32 boards.

💻 Core Arduino Logic

🛠 Libraries & Setup

Start with including Wi-Fi support:

#include <WiFi.h>

Define sensor pins and Wi-Fi credentials:

#define TRIG_PIN 5
#define ECHO_PIN 3

const char* ssid = "yourWifiSSID";
const char* password = "yourWifiPass";

☁️ SMS API Configuration

Your API key, mobile number, and optional message variables go here:

const char* apiKey = "YOUR_API_KEY";
const char* templateID = "103";
const char* mobileNumber = "91xxxxxxxxxx";

📡 Sending the SMS

Once motion is detected, the ESP32 connects to the SMS API and sends a JSON payload containing your message.

🔄 Main Loop

In loop(), you continuously measure distance and trigger sendSMS() when the threshold is crossed:

float dist = readDistance();
if (dist < 100 && !alertSent) {
   sendSMS();
   alertSent = true;
}

This ensures SMS is only sent once per motion event.

✔️ Testing & Expected Results

After uploading your code and opening the Serial Monitor:

• You should see Wi-Fi connection updates.

• Distance readings update continuously.

• When motion is detected, you’ll see SMS sent logs.

If SMS doesn’t arrive, double-check your network credentials and API key.

🌍 Real-World Use Cases

This SMS alert system is perfect for:

• Home security alerts

• Parking space monitoring

• Industrial safety notifications

• Tank level alerts

• Livestock & farm monitoring

• Asset theft prevention

🚀 Wrap-Up

With just a tiny Seeed XIAO ESP32, a simple sensor, and a free SMS API, you can build a real-time alert system that fits in the palm of your hand. Whether you’re new to IoT or building advanced automation, this project is a practical and fun way to dive into wireless alerts without extra hardware. If you're looking for more hands-on tutorials, check out these ESP32 IoT project ideas to build real-world applications.