Are there any people who haven't read Harry Potter? Hardly. So I think you'll remember a marauder's map. It's a magic map that allows Harry and his friends to keep an eye on other characters walking in the castle.
Now this Maradeur's Map has seen the light!
Actually, it's a network of digital cameras able to track person's movement and their real location.
The system is able to recognize faces, match clothes and define people's expecting position. All these let you find certain people in the giant building, be they lost or criminals.