Build a Motion-Triggered SMS Alert System with XIAO ESP32 S3 - No GSM Required

Imagine your basement door opens while you're away - within seconds, your phone buzzes with an SMS alert. That's exactly what this project Send SMS Alert using Seeed Studio XIAO ESP32 delivers, using the Seeed Studio XIAO ESP32 S3, an HC-SR04 ultrasonic sensor, and a free cloud SMS API from Circuit Digest Cloud . What makes this approach simple is the absence of GSM hardware. Traditional SMS projects needed SIM cards and bulky GSM shields. Here, the ESP32's built-in Wi-Fi does all the heavy lifting - it sends an HTTP POST request to a cloud server, which handles SMS delivery to any mobile number worldwide. How It Actually Works The flow is straightforward but satisfying once you see it running live: Power on → Connect Wi-Fi → Object detected <100 cm → HTTP POST to API → SMS delivered The ultrasonic sensor fires a trigger pulse every 500ms and measures the echo return time. When something crosses the 100 cm threshold, the ESP32 hits the Circuit Digest Cloud API with a JSON payload — you