Unlocking Charm

Alohomora is a charm that opens locks. It is also able to open doors locked by Colloportus. Some unknown spells make locked doors impervious to Alohomora.

Descriptions of this spell are written down in several books, including The Standard Book of Spells, grade one, where it is described in chapter seven and a spellbook that can be found in the Hogwarts Library. .

Known practitioners

 * Hermione Granger
 * Ron Weasley
 * Harry Potter
 * Lord Voldemort
 * Miriam Strout
 * Unknown Death Eater (possibly Lucius Malfoy)

Successful

 * On 31 October 1981 Lord Voldemort uses this spell to break into the Potters' house and murder James and Lily Potter.
 * Hermione Granger used this spell on multiple occasions: she used it to open a forbidden entrance on the Third Floor Corridor of Hogwarts Castle in 1991, to open the window to Professor Filius Flitwick's office to rescue Sirius Black in 1994, and to open Regulus Black's bedroom in 12 Grimmauld Place in 1997.
 * The Janus Thickey Ward at St Mungo's Hospital for Magical Maladies and Injuries can only be entered by using this spell. Healers and visitors may enter, but patients are unable to get out.
 * During the Battle of the Department of Mysteries the Death Eaters used this spell to open doors shut by the D.A..
 * In 1997, Hermione used this to unlock Regulus Black's bedroom door at 12 Grimmauld Place.

Unsuccessful

 * The door guarding the Philosopher's Stone in 1991 was protected against Alohomora; a winged key was necessary to open it. A single door in the Department of Mysteries was impervious to this spell as well. It is the door which presumably conceals the room where the Ministry of Magic studies the power of Love.
 * In 1996, Harry assumed that Umbridge's office door had been bewitched so that this spell wouldn't work.
 * In 1996, Harry Potter tried to use the spell on the Hogwarts gates with no effect, as Albus Dumbledore had bewitched the gates.

Etymology
J. K. Rowling stated that the word was from the West African Sidiki dialect used in geomancy and has the literal meaning Friendly to thieves.

Behind the scenes

 * Although Dolores Umbridge's office at Hogwarts was (assumed) impervious to this spell in the novel, Harry Potter uses this spell to open it before attempting to use the Floo Network in the film adaptation of Harry Potter and the Order of the Phoenix.
 * As it was described in a textbook, this may be learned in Hogwarts Charms classes in the first year.
 * This may be the spell that Remus Lupin used to open a wardrobe containing a Boggart, and the spell that Harry Potter used wandlessly to open his cupboard to retrieve his school supplies.
 * In the movie version of Harry Potter and the Prisoner of Azkaban, instead of using Alohomora to help Sirius Black escape, she uses Bombarda to blast open his cell door.
 * In the Chamber of Secrets video game for Gamecube, Xbox and PS2 it's specified that alohomora is for use on mechanical locks. In most other sources, it's used on magical locks and the spell colloportus as well.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Philosopher's Stone (video game)
 * Harry Potter and the Chamber of Secrets (video game)
 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Prisoner of Azkaban (video game)
 * Harry Potter and the Goblet of Fire (video game)
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Half Blood Prince
 * Harry Potter and the Deathly Hallows
 * Harry Potter: Spells

Notes and references
Alohomora Алохомора