Enchanted coin

Enchanted Coins/Galleons are used for communication. Hermione Granger created them in 1995 to inform members of Dumbledore's Army of the next meeting. Draco Malfoy copied the idea in 1996 to communicate with Madam Rosmerta, whom he had placed under the Imperius Curse.

History
Hermione fabricated fake Galleons, on which she then placed a Protean Charm. Around the edge of each coin was a series of numerals which represented a serial number belonging to the Goblin that cast the coin. The Protean Charm allowed these numerals to change into the time and date of the next meeting of the DA whenever the master coin, owned by Harry Potter, was changed. The coin would also warm up to alert the holder to the change.

In 1996, Draco Malfoy uses a pair of enchanted coins to bypass the communication limits then placed around Hogwarts, thus managing to keep in contact with Madam Rosmerta, whom he had placed under the Imperius Curse. Draco reveals he got the idea from Hermione's Dumbledore's Army coin, which were themselves inspired by Lord Voldemort's use of the Dark Mark to communicate with his Death Eaters.

In 1998, Neville Longbottom used the coins to summon former members of Dumbledore's Army to Hogwarts School of Witchcraft and Wizardry to fight the Death Eaters and reclaim the school. The former members alerted many others, including the Order of the Phoenix, and set the scene for the Battle of Hogwarts.

In later years, the surviving members of Dumbledore's Army would keep their coins, regarding them as badges of honour.

Use
Like real Galleons, the coins have numerals around the edge; on normal Galleons these serial numbers indicate which goblin cast the coin, but on the enchanted coins, the numbers represent the time and date of the next meeting, and change automatically to match whatever numbers the user sets on his coin. The coins become hot when the numbers change to alert the members to look at their coins.

Appearances

 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows