Well first of all its just an audio signal. I can open my 2006 Accord from 100s of miles away over a cell phone as long as the person on the other end is close enough to the car, or the more fun thing to do is hit the panic button, and listen to your car honk at them while they scramble for the spare set of keys you left them. Its actually a pretty cool trick in this day and age of cell phones, because if you lock your keys in your car, you can just get someone with the spare keys to open if from very far away.
-Tig
