In this project, we created a geofencing project using Arduino and the Adafruit FONA 808 breakout board. We saw how to set an alarm if the project was going beyond a given distance, and we also connected the project to Adafruit IO.
You can of course go further & mix the two projects together, to have both the alarm and the tracking via Adafruit IO. You could also think for example about forbiden zones on a map that would also raise an alert. Finally, you could also connect the project to IFTTT, to automatically send you notifications in case the fence is breached.