Two-way mirror
A pair of mirrors that served as communication devices between two people, one with each half. James Potter and Sirius Black had enjoyed using a pair of mirrors to speak to each other in detention at Hogwarts. Years later, Sirius gave Harry the half originally owned by James. The second half later came into the possession of Aberforth Dumbledore, who used it to keep an eye on Harry during the events of Deathly Hallows - he therefore knew when to send Dobby to Harry's aid at Malfoy Manor.
