The BC817 is a NPN/PNP transistor manufactured by High Diode, typically in SOT-23 form factor and RoHS compliant. It is used as a general purpose amplifier/switch in various application like audio, power and signal switching. It can handle up to 500 mA current, has a breakdown voltage of 55 V and a maximum collector-emitter voltage of 40 V. It is reliable and efficient, making it a popular choice for cost-sensitive applications.