The light barrier system described in this article allows accurate measurement of the absolute speed of model cars, planes and other moving objects. In education and training programmes, the system forms a perfect contactless speedometer. Over to you to football and golf fans to see who has the meanest ball kick or club swing.Light barriers systems are around us in more situations than you would expect. Unnoticed, they do their job scanning items at the supermarket checkout, detecting vehicles in parking lots, video tapes in VCRs or persons entering or leaving buildings. Usually, infra-red light is employed because it is invisible to the human eye and ensures a high degree of immunity against interfering light sources.