A method and system to monitor and determine energy consumption and energy efficiency of devices that use electrical and/or gas power is described. In one embodiment, a power monitoring system is configured to monitor electrical and/or gas power consumption of devices such as refrigerators, air-conditioners, washers, dryers, hot tubs, etc. Power consumption of the device is processed by the power monitoring system to determine the amount of power the device is consuming and the device's energy efficiency. In one embodiment, the power monitoring system transmits data associated with the device's power consumption, such as power efficiency, power cost, power usage, etc., to the device user and/or to a power supplier such as a utility company supplying the gas and/or electricity to the device. In one configuration, when the power efficiency of the device exceeds a predefined threshold, the user and/or power supplier is notified. The power monitoring system may be configured to be integral with and/or attached to the device being measured. The power monitoring system may provide an output on a display apparatus associated with the power monitoring system attached to the device being monitored and/or the output may be part of a graphics display on a computer monitor, for example.