A rim lock is a locking device that attaches to the surface of a door.
It is the oldest type of lock used in the United Kingdom and Ireland. It is of a basic design using (usually) a single lever and a sliding bolt. Wards can be used for additional security. They are not used where high security is required. Most older locks were large, some as big as 40 cm by 25 cm. Most rimlocks used today on exterior doors in the British Isles are night latches.