Scabbydug coughed up some electrons that declared:


Cylinder with thumbturn is the general term, in premises such as hotels &
guest houses the fire officer usually insists on them.
On external doors in private properties the insurance companies are a bit
iffy about them, if someone breaks in through a window for instance, they
can open the door from the inside and let their mates in and escape
easily with the loot.

Oh - and to consider the "thumbturn" aspect:

Had one of these on my last flat - it was backed up with a mortice lock.

I leave the key in lock at night to aid escape in a fire.

I also reckon, that if the burglimen get in your house, it's better to give
them a direct means of escape. That way, should you surprise them in the
act, you've got a better chance they'll take flight out the door, rather
than finding it deadlocked, being trapped between you and it then coshing
you on the way past (cornered rat syndrome).

Cheers

Tim