I may be mistaken but I know with some cars with keyless entry, you can use the key to open it like a regular lock in case the keyless system fails for some reason.

My roomie works at a gas station and he said that one lady had her keyless system batteries die in the key fob thingie. She was like, "OH NO I CAN'T GET IN MY CAR AND MY BABY IS IN THERE!" He asked to see the key, walked over to the car and opened the door manually and she stood there gawking at him as if he had just performed a miracle.