lucy24 - 12:18 am on Sep 6, 2011 (gmt 0)
How 'bout this way.
You leave for a long vacation, and in the excitement of the moment forget to close your back door. By and by a neighbor notices, closes and locks the door. And then leaves on a vacation of his own, overlapping your own absence, or simply forgets all about it.
If they leave a note on your kitchen counter saying "I locked the door on such-and-such date", you are alerted to the possibility of Something Bad having happened before then. If not, you may never know that you left the door open. Until months later, when you look for a special piece of jewelry and find the box empty.
Then again, if the kind neighbor had a warped sense of humor they would lock the door-- but only after rearranging your furniture, adjusting the curtains and putting your pictures upside-down.