Optex AX-250PLUS photobeams is cost-effective long-range dual beams for internal or external applications. Suitable for external ranges up to 150m outdoors, the beams have twin infrared transmitters and receivers to reduce the potential for alarms from small animals, blowing debris and falling leaves. Beams operate by only triggering an alarm when both beams are broken simultaneously. Model: AX-250PLUS : 75m. Model: AX-500PLUS : 150m