The key fob uses rolling code technology for locking/unlocking the door(s). In some systems, after a few hundred signals from a commonly used transmitter, an unused transmitter will no longer have it's signals recognized. I'm not sure if this is true for the Crossfire, but it is possible, and I would use the infrequently used key fob once in a blue moon to unlock the door(s). It could always be reprogramed if it is nolonger recognized. As far as starting the car, that involves another electronic circuit - an RFID chip - and the key should start the car without any problem even if the fob is no longer recognized.