Kemo b213 infrared light barrier kit with 50m range kemo b213 p this solder yourself kit has a working range of up to 50m made possible by the special optical system and highly sensitive photo receiver the infra red beam is invisible to human eyes and is therefore perfect for security and surveillance p p when the light beam between the transmitter and the receiver is broken e g by a person the relay in the receiver operates and can switch on whatever is connected to it for examp