GB wrote on 31/05/2018 :
We have a night latch - one of these:
https://www.ironmongerydirect.co.uk/...-chrome-850075

What is the best way (ie easiest, not necessarily cheapest) to convert this
to combination lock?

The easiest way, is to use an electric one. You would need to replace
the part which fixes onto the door frame (the latch ?), with a solenoid
operated version, then add a suitable keypad and logic somewhere near
the door.

I have one on the small side door of my garage. Which operates on 18v
DC from memory. You can set it with 6 to 8 number /letter code entry,
with four different user codes and a master code. So four different
people could have their own different entry code, one person leaves the
company, so just their code needs to be changed to a new one for a new
person.

Type one of the correct codes in and power is applied to the latch to
release it it hinge out of the way, but only for a preset few seconds
when it re-locks. A normal Yale type key can also be used as usual.

I got fed up of needing a key to get into my garage/workshop, so added
this instead. Now I just need to remember the entry code. I get in
fine, if I do it without thinking, but struggle to remember the code if
I think about it :-?