My Salt Lake friends knew their house guests would arrive in town during working hours. Since they couldn't get out of work to welcome their guests, they sent them a set of house keys in the mail. It was their guests' first time in Utah, so they included a detailed map from the airport to their house. They dropped the package in the mail 10 days before their friends would leave the east for Salt Lake. It should have taken four or five days to get there, so after five they began to get a little concerned. The suspense heightened after each daily phone call asking, "Did the package arrive yet?" In 10 days it still hadn't arrived, and the postal service had no idea of its whereabouts. At this point they're faced with a choice: Spend the money and resources to replace all the locks, or hope that the map and keys to their home didn't fall into the wrong hands. I think that the vast, vast majority of human who get mail would not break into someone's home even if they were given a treasure map, key, and time that the family would not be home. And my friends' family agreed with me. They never replaced the locks, and no one's broken in. They also haven't had the mail returned, so it's still out in the ether somewhere. So if you ever get that mail with the key and map, now you know the house is there and the key still works.