OPB816Z Optek, Panel Mount Slotted Optical Switch, Transistor Output

Optek OPB816Z slotted optical switch offers a robust sensing solution with integrated dust protection. The optical switch consists of an infrared emitting diode and an NPN silicon phototransistor, mounted in an opaque housing.
Switching takes place whenever an opaque object passes through the slot.

Slotted Optical Switches, Optek Technology