We can use GPS in our phones to track them if they're ever lost or stolen, why not do the same with your car? This DIY solution uses an Arduino Uno, a GPS module and a GSM shield to send you text messages and updates as the car is on the move.
Instructables user Javis Vineer Gonsalves wanted a way to tell authorities exactly where his car was if it was ever stolen, so he put this system together. All told, it's not terribly difficult to do, especially if you have a little experience with electronics projects. When you're finished, you'll have a low-cost GPS tracking system that doesn't require a pricey subscription to a third-party tracking or security service. It also has the benefit of being able to show you where you parked, if you ever forget, without having to set up an app or install anything special.
Of course, you could also hard-wire a phone to a car charger and use it to do something very similar, essentially making the phone the locator, but this is a bit less pricey than potentially throwing away a good mobile phone, and it's much more power efficient. Another perk with this method -- while it's designed for a car, it's easily adapted to anything else you might want to track. Hit the link below for the full walkthrough and step-by-step build, along with the code required to get it all working.
Athena: The Global Car Tracking System [Instructables]