How these vehicles work is a bit mysterious, but we're sure your children will love watching this fire truck and train drive around and around their drawings. A small optical sensor on the bottom allows the vehicles to follow any thick black line made from a marker or crayon on a white piece of paper. Each vehicle includes one black marker, a test track, operating instructions and 4 button AG13 batteries. This item measures 3-1/4" long x 1-3/4" wide x 2" high.