How do self locking front doors work?
different internal mechanism ... gravity drops a pawl into the lock as soon as one removes the key. The latch mechanism allows the door to close, but it is then locked. you can't change this behavior without changing the lock entirely.
this fact will vary depend upon the mechanism that has been used
Not as well as a pack of French Mastiffs.
In many cases, self locking is a bit of a misnomer. The lock is actually ALWAYS locked and the key only retracts the latch allowing the door to open.