Travel security Door guard by  Howser is a great way to lock a door from the inside, it is smal light and is manufactured out of a very strong plastic.
The lip is placed in the latch recess of the door frame, the door is closed and then the curved hook is placed through the exposed hole in the plate and pushed up until it will go no further.
It can be inserted and removed in seconds and once in position prevents the door from being opened. It is an ideal device for anyone staying in hotels, apartments, rooms or anywhere you may encounter dodgy locks, faulty catches, duplicate pass keys etc.
The Quick lock  can also provide privacy for parents/teenagers and and makes perfect presents for the elderly.