Photo Beam 200/400M Quad 4Ch. The Photobeam four channel quad beam ISC-FPB1-W200QF detector with separate transmitter and receiver. The detector uses four pulsed infrared beams that are designed to activate an alarm when all four beams are simultaneously blocked. False alarm immunity is increased by the utilization of four beams compared to single or dual beam models. The detector is also features interlocked upper and lower beams, signal voltage LED, and optional environmental discrimination circuitry.