The key, if you take it apart, has the circuit board, battery, metal key part (which is removable) and a small grey tube nestled away in the plastic, but is visible and removable.
Its not a powered part, it is a passive oscillator that vibrates at a certain frequency when excited by the ignition electronics. It is easily foolable, by just getting another oscillator to fool the ignition at the right frequency, which is why these cars can still be stolen.
Like 986 said, you need to know the accessory wires, ignition wires and proper grounds, but that isn't too hard to find (or to figure out with a multimeter).
I thought about doing the push to start, but then I wised up a bit and now my fingerprint starts my car
