Global Dragon Radar is a Dragon Radar that is a giant map of the Earth that only reveals the general area of a Dragon Ball. It does not show the exact spot of where the Dragon Ball is, unlike Bulma's. The Red Ribbon Army have one in their command room, which is where they were able to follow Goku.
In Dragon Ball: Mystical Adventure, Master Shen has Pilaf, Shu and Mai build one for him. Pilaf and his gang have a Global Dragon Radar in their airship, which they use to help King Piccolo and his sons find the Dragon Balls.