I've been told many reasons for doing so over the years: common thieves, serial killers, Arab workers, teen-aged hooligan neighbors...but this one surprised me. I went out the door and found, in the driver's seat of my car, my two year-old. He had managed to climb in, close the door, turn on the radio, and was trying to figure out how to put the car in motion when I caught him. And just when I thought it was safe to live in a small town... Yes, I will be locking my doors from now on.