Most cars have a physical key tucked in the fob, and will do some form of passive RFID “auth” when the fob is brought close to the start button or equivalent. It is not too different from engine immobilizer keys.
I'm aware of the key in the fob. I Wasn't aware that there were other capabilities if the fob itself wasn't working. Was just experimenting the other day about the capabilities and limitations of the keyfob under different conditions.
It seems as if you can't lock the key in the car but I'm not sure how much I trust that experiment.
