For many years, where my grandmother lived (in Lexington, TN), she kept her front door unlocked. This was long after my grandfather had passed away. She still had neighbors who might need to come in and borrow some butter or something.

After a long time, she started locking the door. But she left a copy of the key in the mailbox next to the front door. That was also for her, in case she went out and lost her keys or forgot where she put them.

It was only a few years before she passed away that she had the key taken out of the mailbox.