A Time Turner is a time-traveling device in the Harry Potter universe. It is usually worn around the neck as a necklace. The Time Turner used by Hermione in Harry Potter and the Prisoner of Azkaban required rotations to be made for each hour one decides to go back in time. However, in the narrative of this book, it is shown that time turners don't change the past. They only allow one to go to the past and do anything that matches the continuity of the real world without any time paradoxes.