Walk out of range and the car automatically locks when the connection drops. His build uses an Arduino Mega with a BlueSMiRF Silver Bluetooth board that actively searches for his phone and ...

The $22 kit includes an Arduino-BLE board and 6-pin header that should be fairly broadly applicable for building Arduino-based hardware that can communicate with iOS devices.

Unlocking your car isn't exactly tough, but if you want to spice it up a bit, The Mercuino Project shows off how to unlock your doors with Bluetooth and an Arduino.