In Robot Tag, by Caitlin Hall, Becky Lippmann, and Claudia Wagner two robots play tag. Each has light sensors that can detect the white light bulb on top of the other. The "hunter" (the robot that is "it", designated by a red light) chases the other robot, which tries to run away. If the two robots touch, they switch roles. If a robot hits a wall, it backs up, turns, and continues forward.