Participating phones are positioned in a stack, each phone held by a different player. The top phone's screen displays its camera's viewpoint, overlaid with a maze incorporating an AR tag, and a ball guided by accelerometers. When the ball is guided to the end of the maze it 'falls' through a hole, at which point the second phone can 'catch' it, but only if it is positioned correctly. At this point the phones swap positions to continue the game.