Effective ranging linkage between in-vehicle gadget

Furthermore, actions such as locking or unlocking the doors, starting the ignition, and choosing preferences such as climate, seating adjustments, multimedia selections, and other user-specific profiles can be set when the driver approaches or leaves in-vehicle. NFC leverages the principle of magnetic induction to establish a communication link between two devices employing loop antennas. The effective range of link is no more than a few centimeters, so in-vehicle the user experience for setting up the connection is built around close proximity or touch. 

refer to: http://embedded-computing.com/articles/wireless-accelerate-next-wave-in-vehicle-innovation/