A power measurement device in accordance with aspects of the invention comprises a power harvesting unit that extracts a fraction of current flowing through an electric power supply unit to an electronic appliance; a power determination circuit that generates power measurement data indicative of at least one of the extracted current or a power consumed by the electronic appliance determined based on the extracted current; and an output device that outputs the power measurement data. The power measurement device can be used with plugs or sockets as an external component or integrated therein as an internal component.