The other day I had to help out someone who had lent a guest a set of keys and the guest had dealt with the set on departing by posting them into the apartment’s mailbox. Problem was – that set happened to have the only copy of the mail box key. I think I posted about a similar story but it would have been about ten years ago.
The second story also concerns locks with only one copy of the key. This time the only copy of a deadlock key is held by someone other than yourself. And one day you come home to find that the “never used” deadlock has been locked. If there’s a deadlock on one of your doors – flat door, communal door or both – either determine that it’s completely inoperable or that you get a key.