The ITR8307/S18/TR8 Photo Interrupter SMD-4 RoHS, manufactured by Everlight, is a small surface mount device that detects the presence of objects passing between the gap of an integrated infrared LED and NPN phototransistor. This device works by emitting infrared light from the LED towards the object; when the object passes between the gap, it will block the light from entering the phototransistor. This will cause a decrease in current to the LED, triggering the NPN phototransistor to switch from open to closed. The ITR8307/S18/TR8 device is constructed of reinforced plastic to help protect it against damage and can detect objects up to 10mm away. Additionally, its RoHS rating ensures that it meets the severe environmental safety regulations required for use in much of Europe and the U.S.