Traditional GPS trackers are expensive to build- they typically require a SIM card, a GSM module, and a cellular data plan just to send a location ping. For hobbyists and engineers building prototypes, that overhead kills momentum fast.
This project Send SMS Alert using Seeed Studio XIAO ESP32 changes the equation entirely. Using the Seeed Studio XIAO ESP32-S3 paired with a Neo-6M GPS module, you can build a fully functional, real-time GPS tracker that transmits over Wi-Fi - no SIM card, no GSM module, no cellular bill.
The system connects to the free GeoLinker cloud platform by Circuit Digest, which stores location history and visualises your route on an interactive map. The standout feature is built-in geofencing with SMS alerts - the device monitors a virtual boundary and fires a text message the moment it is crossed, including the exact coordinates of the breach.
It even buffers data locally when Wi-Fi drops, syncing automatically once reconnected. For under a few dollars in hardware and zero in subscription fees, this is one of the most capable entry-level trackers you can build.
Key Features
•No SIM card or GSM module required - transmits over Wi-Fi
•Real-time location updates every 15 seconds (adjustable 1- 60 s)
•Geofencing with configurable radius (10 – 5,000 m)
•SMS alerts with exact coordinates on boundary breach
•Offline data buffering - no location data lost on Wi-Fi drop
•Free GeoLinker cloud - 10,000 data points at no cost
•Interactive route map with full location history
Components Required
Component
1. XIAO ESP32-S3
2. Neo-6M GPS module
3. External GPS antenna
4. Breadboard
5. Connecting wires
Software
• Arduino IDE
• GeoLinker Library - cloud communication
• TinyGPSPlus Library - NMEA sentence parsing
• WiFiClientSecure - HTTPS connections
Setup Overview
1.Wire the hardware. Connect Neo-6M TX → GPIO 44 (RX) and RX → GPIO 43 (TX) on the XIAO. Power the module from the 5V and GND pins. Attach the external GPS antenna.
2.Create a GeoLinker account. Sign up at circuitdigest.cloud, navigate to My Account → API Keys, and generate your free key. New accounts receive 10,000 data points at no cost.
3.Configure the firmware. Paste your Wi-Fi credentials, API key, device ID, and home coordinates into the sketch. Set your update interval (default 15 s) and geofence radius (default 50 m).
4.Flash and test. Upload via Arduino IDE. The ESP32-S3 will connect to Wi-Fi, parse NMEA sentences from the GPS module, and push coordinates to GeoLinker every 15 seconds.
5.Watch the map. Open your GeoLinker dashboard to see live position dots and route history. Cross the geofence boundary to verify the SMS alert fires with your current coordinates.
How Geofencing Works
The firmware uses the Haversine formula to calculate the straight-line distance between the device's current GPS position and the home coordinates defined in the code.
•Distance > geofence radius → SMS alert sent with current coordinates
•Device returns inside boundary → alert flag resets
•Device crosses boundary again → new SMS alert fires
The SMS is delivered via the Circuit Digest Cloud SMS API to the mobile number specified in your GeoLinker account, containing exact latitude and longitude at the moment of breach.
Real - World Applications
- Vehicle & Fleet Management
- Asset Protection
- Child Safety
- Elderly Monitoring
- Pet Tracking
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