Using an Arduino, hacker knowledge and a Nike+ iPod Serial to USB adapter, Nathan Seidle was able to rig up a system that constantly checks for his keyfob. When Nate gets close enough to his car, it opens up. When he walks away, it locks. The system worked flawlessly until he realized that while at work, the car would randomly lock and unlock due to his pacing around the office. The fix? Aluminum foil. A classic solution to blocking radio waves. If you want to make your own, instructions are available.