The back door lock has always been a bit of a puzzle.

In a UPVC door.
One full turn and the door is locked but the handle is still floppy.
Another full turn and the handle firms up.
Another half turn or so before it seems to finish locking.

I don't think I have ever encountered a lock with so many turns between
locked and unlocked.
I would normally expect all this to happen within 3/4 to 1 1/4 turns.

The lock is now refusing to unlock from the second turn to the first turn
without a lot of juggling, cursing, swearing etc. so I am about to take it
out and try and get a replacement.
Lubrication via the key this morning made it worse instead of better.
If locked on the first turn only it seems fine but if you overshoot then it
is a lot of hassle.
Not good if you want to get out in a hurry!

There is also a stranger little black box on the door which looks like some
kind of burgalar alarm.
It has 'Semco' as a name on the little lock (we don't have a key) an on/off
sliding switch and something that looks like a stereo jack socket.
The oblong box also has a spy hole (as it is mounted high and near the door
jamb and there is a step down as well I can't see how you would ever see
anything useful).

Google finds a Semco alarm which is battery operated (although not like
ours) so I am hoping that it is not connected in any way to the door lock!

Wierd to have this on the back door but not the front, although the back
door may be older than the front door.
Possibly a legacy of owner -2.

The runes of doom keem coming up with "Specialist lock integrated in door.
New door please."
I am trying to ignore them and will sacrifice a virgin for an alternative
reading (although sourcing one may be a problem around here).

Cheers

Dave R