It's happened so often that I just carry a second key with me whenever I go anywhere with it. Just yesterday I took the car to my photo spot, left the key in the ignition and got out to take pictures and when I tried to open the door it was locked. It happens if the car is running or not, keys in the ignition or not. The owners manual mentions Automatic Door Locks but that's just when the car reaches 15 mph. Anybody have a similar problem with a Nissan?