Remote vs. Key

Ruth says her mom called her once at work. Mom had been at Ruth's house, but when she tried to get back in her locked car, the remote wouldn't work. So Mom had to walk the six blocks home to get her *other* remote, then walk the six blocks back to the Ruth's house to get her car. Ruth asked her, "Mom, why didn't you just use the car key on your key ring to get in the car?"