I was hoping there was a way to have the keys programmed to work on both cars, but that does not sound possible. As an alternative, how do others identify their keys? We will be adding a second Model S to the family (at least for now). I like to have my key as is without anything on it. My wife keeps hers in the Tesla case that came with the car. Also, I noticed when we had a demo car that when I press the button on the charger cable the charge port (on both cars) opens. Even if the second one is parked outside.