Alohomora: the Unlocking Charm

Alohomora is the Unlocking Charm, a Charm used to open certain locks on objects. Most basic doors and windows can yield to it, while a protective charm placed on a lock can block the attempt. 1

Its clearest first-year canon anchor is the forbidden third-floor corridor. While hiding from Argus Filch, Hermione uses Alohomora to open a door, only to find Fluffy, the three-headed dog, on the other side. 2

The paired file is Colloportus, the Locking Charm. It seals doors, and the official fact file identifies Alohomora as the charm that can counteract it. 3

The quick memory is simple: a basic lock may yield; a protected lock may hold.