The Unlocking Charm (Alohamora), is a charm that can open mechanical locks.
It can also open doors that are locked by Colloportus.
Several unknown spells casted on some doors and locks do not allow Alohamora to open them.
Descriptions of his spell are written down in several books, including The Standard Book of Spells, a spellbook found in the Hogwarts school Libarary, in chapter seven.
|Lord Voldemort||The Potter House door|
|Hermione Granger||The door to Fluffy's Corridor|
|Ronald Weasley||The locked door to the Giant Chess Board chamber in the Philosopher's Stone Chambers|
|Harry Potter||The door to Dolores Umbridge's office. Failed attempt.|