Night latch

A night latch is a lock that is fitted on the surface of a door; it is operated from the exterior side of the door by a key and from the interior side of the door by a knob.

Overview

Night latches are usually rim locks and are available as deadlocking and non-deadlocking versions.
Historically, such locks were intended for use at night-time, hence the name. The keyless egress that they offer is a valuable fire safety measure, but may be a security risk if breaking a glass panel or a nearby small window allows an intruder to reach the knob inside and open the door from the outside.