This infrared phototransistor conducts current when exposed to infrared light. The pin connections are the collector and emitter pins. There is no base connection pin as this is enclosed inside the device and controlled by infrared rays incident on the device. This device has been designed to suppress the sun infrared light but respond to infrared light from an infrared light emitting diode. Pair this device with an infrared light emitting diode for your proximity detection projects, remote control projects, heart-rate monitoring/measurement projects etc.