Defining and Measuring Standby
Definition of Standby
Most people think of standby as the energy consumed by a product while switched off or not performing its primary function. This kind of definition is unsuitable for technical and legal purposes and a more precise definition is under development by the International Electrotechnical Commission (IEC) and other groups.
The original IEC definition (and the U.S. Presidential Executive Order) defined standby as a product's minimum power consumption while plugged in (sometimes called the "off mode" consumption). This definition doesn't distinguish between products that are truly doing nothing and others that are providing some sort of function in this lowest power mode, such as waiting for a signal from a TV's remote control or the operation of an LED status light.
Few products indicate their standby power use, so you need a meter to measure it. Unfortunately, few meters have sufficient resolution to measure standby power accurately. These cost over $500.
A few meters are now available for less than $100. Unfortunately their accuracy below a few watts is poor. These are nevertheless indicative of standby power. You can improve accuracy by adding a standard load (such as an incandescent light bulb) into the circuit; then measure the difference in power consumption.
One definition of standby is the power draw of an appliance in its lowest power mode. For appliances with a power switch, we measure the power draw while the unit is "off". For appliances without a power switch, such as cordless telephones, answering machines, and battery chargers, power draw is measured while the units are plugged in, but are not being used by the consumer.
Some appliances' main function, particularly those involving communications, must be performed at all times. For example, network hubs continuously transfer data from one part of a computer network to another. In this case, we measure the power draw of the appliance while it is not connected to the network. This ensures that the unit is in its lowest power mode.
A few appliances are much more difficult to measure. Refrigerators, for example, have hidden functions that can be difficult or impossible to turn off. Since some of these hidden functions are not considered "standby power", it is nearly impossible to get an accurate measurement.
Standby power is measured as an average power draw. This is convenient but not as reliable as when measured over a period of time. Most meters can integrate power use to yield a standby energy use.