I can't recall my parents ever locking the doors on our house when I was a kid growing-up in Northern Michigan. In fact, after all of us kids had left home, my parents decided to take an extended vacation down to Texas to visit some family and friends, and since they were going to be gone for a couple of weeks, they thought that perhaps they should lock the doors when they leave. The problem was, they couldn't remember where they'd put the keys. It took them a couple of hours before they finally found them.
http://www.huffingtonpost.com/2014/09/30/door-locking-poll_n_5889192.html

OCU