Two-way mirror

A communication mirror is a two-way mirror that allows people to communicate with each other between locations.

During their years in school, James Potter and Sirius Black used a pair of communication mirrors to talk to each other while they were in separate detentions. Sirius later gave James' mirror to Harry in 1996. After Sirius' death, his mirror came into the possession of Mundungus Fletcher, who in turn sold it to Aberforth Dumbledore.