Marauders Map

Appearance
The Marauder's Map is a worn piece or parchment, large and square, with nothing written on it until activated. Once activated, it is a very detailed map of Hogwarts and its surrounding grounds, with these large words written in green ink on the top of the parchment:

Messrs. Moony, Wormtail, Padfoot, and Prongs

Purveyors of Aids to Magical Mischief-Makers

are proud to present

The Marauder's Map

Function
Not only a detailed map of Hogwarts and its grounds, but also a foolproof surveillance system, with the movements of everyone in the castle displayed as tiny dots with names. It shows the seven hidden passages from Hogwarts, and can even tell you the identity of someone disguised with Polyjuice Potion, invisibility cloaks, or in Animagus form. It will even go so far as to show the Mischief-Maker what actions they need to take to get where they want.

How to Use
Touch your wand to the parchment and say "I solemnly swear that I am up to no good", and the map will be revealed. To clear, tap the parchment with your wand and say "Mischief managed". Forgetting to clear the Map can lead to great troubles, as Harry learned the hard way on more than one occasion.