The key to our Challengers have a built-in transponder hidden inside. When a key is inserted into the ignition lock cylinder and turned, the car's computer sends a radio signal to the transponder. Unless the transponder replies with a valid code, the computer will not allow the engine to be started. Transponder keys have no battery; they are energized by the radio signal itself.

I found a video which demonstrates what happens if a key is inserted into the ignition cylinder without a transponder (i.e., same as hotwiring). Very interesting. See:

http://www.youtube.com/watch?v=bc1_VvbewDs