How to Build a Spy GPS Tracking System
Posted on April 29, 2008 by jaiz
The Open GPS Tracker is a small device which plugs into a $20 prepaid mobile phone to make a GPS tracker. The Tracker responds to text message commands, detects motion, and sends you its exact position, ready for Google Maps or your mapping software.”
The current supported hardware platform is:
- Tyco Electronics A1035D GPS module
- Motorola C168i AT&T GoPhone prepaid mobile phone
- Atmel ATTINY84-20PU AVR microcontroller
[more]
source: opengpstracker.org

I see two potential issues: 1) the GPS antenna needs to be placed a location where it can see the sky (the satellites) in all directions, and 2) I have no one to spy on