E3JK-R4M1 DC 12-24V 4m sensing 18x50x50mm retroreflective photoelectric switch with reflector E3JK series photoelectric sensor. E3JK-R4 series prism relay photoelectric sensors. E3JK-R4M1: align to reflector, the LED is not light, when an object is between them, the LED will light.
eBay