here is a interesting idea every thought of opening your car with a smartphone, by 2015 this may be happening.
here is a quote from http://mashable.com/2012/12/28/nfc-smartphone-car-keys/
South Korean Hyundai Motor Company predicts by 2015 drivers will be able to unlock car doors and start the engine with a swipe of a smartphone over an embedded near-field communication tag.
But, that’s not all your smartphone can do. Connected car systems will be able to detect your phone automatically to stream your favorite music, phone contacts and radio station preferences seamlessly. Seat and mirror settings will also automatically change depending on who is at the steering wheel. The best part is your battery will wirelessly charge while it’s sitting in the center console, according to Hyundai.
all I can say is don't loose your smart phone or you will not be able to enter your car