The Hyper Line Tracker (infrared sensor robot kit) possesses a sonic tracking system, and is fortified with a multitude of sensors: photo transistors to detect a black line, tracking memory to memorize its last track of the black line, and two red LEDs that to tell you which side of the light sensor is activated. Hyper Line Tracker follows a designed course. By using an infrared emitter, light sensor circuitry, and tracking memory, it demonstrates how robots "see" a pathway. Make a path with a black felt tip marker or black tape and watch how infrared sensors enable the robot's motors to make course corrections. Printed circuit board pre-assembled, no soldering required. "AA" x 4 each (not included).  WARNING: CHOKING HAZARD - Small parts. Not for children under 3 yrs.