I personally don’t like being able to lock myself out of my house . . . .  if we had a simple yale design that locked as soon as we closed the door, that would be possible.  However, when we moved to this current house, it had the superb deadlock design.  So when we close the door to lock it, we have to lift the handle firmly – this operates deadlock bolts at the top and bottom into the door frame, then we can lock with a key as normal.  This is the same whether locking up inside for the night, or on the outside when we’re going out.   So we cannot get locked out if the door slams shut before we’ve taken our key with us.  I was trying to explain this principle to a very aged pal of mine.  She was convinced she had the safety system.  She did used to have before she was talked into having a fancy new front door fitted  – that just has the yale key instant lock system – very much a backward step by my recokoning!