ABS series circle & relay style active photoelectric detector is different from those detection available on the market, it adopt one-side receiving and the other transmitting relay structure and CPU control, with makes each unit linked, not separated. Among these detectors, No.1 is with 6 connection extremity, (power , tow-zone alarm output ) while No. 2,3,4 need only to be connected to the power supply . This detector is specially designed for swimming pool protection.