Optek, OPI1280-026 DC Input NPN Phototransistor Output Optocoupler, Through Hole, 4-Pin

The OPI1280 series of fibre optic isolators consist of a red LED and a phototransistor sensor. They are housed individually and coupled by a fibre optic cable. Their opaque package seals and protects the optical signal from dust.
Suitable applications for the OPI1280 series include; electrical isolation, industrial equipment, medical equipment and applications that require high voltage isolation between the input and output.

Optocouplers, Optek