A nightlatch also known as a yale lock, is fitted on the internal side of a door and will help give the door more sturdiness and keep it closed when in a locked position. We recommend that you always combine your nightlatch with an insurance approved deadlock.
A mortice deadlock operates only with a key, unlike a nightlatch (Yale lock) which can be operated without the need for a key. Deadlocks are typically found on wooden doors and have a hardened steel security bolt which is fitted inside the door. The bolt inserts into a secure point (strike box) in the door frame, when locked.