Having read this thread from the very beginning, I cannot find any reference to adding a key card. I realize the question was about a key fob, but will this work with a key card? I don't own a key fob, but I'm planning on several trips renting am M3 and don't want to drag that really big plastic encased card around. If I bring one of my cards, can add it to the rental? I cannot think of a reason why not. Has anyone actually tried it?