Often referred to as 'Yale' locks, 'nightlatches' are hugely popular due to their versatility and what we refer to as a 'privacy facility' allowing the door to be unlocked while still preventing access from outside. They can be fitted to both internal and external wooden doors and are readily used in shared houses such as student accommodation. 

Be careful as these locks, because of their method of operation, are responsible for a large percentage of lockouts! Check you have your keys!!