Used to signal the start of the Triwizard Tournament tasks
A cannon is a piece of artillery typically used as a weapon, although they are also commonly used for ceremonial purposes. A cannon was used at the start of each of the three tasks during the 1994 - 1995 Triwizard Tournament. Hogwarts Caretaker Argus Filch fired it, signalling the contestants to proceed to the task. On several occasions, he accidentally fired the cannon before it was time for the champions to proceed to the task.