What's a watt?

People often get confused about the difference between watts (W), watt-hours (Wh) and kilowatt-hours (kWh). A watt is a unit of power (1 horsepower = 746 watts), whereas watt-hours tell you how much energy is used over a period of time. For example, a 100-watt light bulb uses twice as much power at any given moment as a 50-watt bulb. To find out how much electricity that light bulb consumes, you need to know how long it's left on (watts x hours, expressed in watt-hours). To get kilowatt-hours, simply divide watt-hours by 1,000 [sources: Bluejay; Newton].

What is phantom power?

Also called phantom energy, phantom load, standby power, idle current and vampire power, phantom power is the energy used by appliances and electronics when they are turned off but still plugged in to a power outlet [source: Energy Star]. According to the Lawrence Berkeley National Laboratory (LBL), the average home contains 40 products constantly drawing power. Individually, the electricity flowing to a TV that's been turned off or a coffeemaker programmed to brew in the morning is extremely small, but together, these sleeping devices may account for as much as 10 percent of household energy use [source: Lawrence Berkeley National Laboratory].

That percentage has actually grown since 1996, when researchers from LBL and Davis Energy Group attributed just 5 percent of residential energy consumption to so-called "leaking electricity" [source: Meier]. Why the increase in wasted electricity when we're supposedly getting smarter about energy conservation? It makes sense when you think about the kinds of devices that consume the most phantom power.

Generally speaking, the biggest phantom power consumers include any device with a remote control (such as a TV, DVD player or garage door opener); an external power supply (that clunky black box known as a "wall wart" on the plug for your router, printer or cable modem); a charger (for a mobile phone, tablet PC, laptop, GPS or handheld gaming device); or a continuous display (an alarm clock, oven, microwave, VCR or coffeemaker with a digital clock). Laptop computers and cable boxes (particularly cable boxes with integrated DVRs) are among the worst phantom power offenders, drawing an average of 9 watts and 44 watts in "off" mode, respectively [source: Lawrence Berkeley National Laboratory].

Older appliances such as ovens without digital clocks, and washers and dryers with manual dials instead of brightly lit consoles, are less likely to draw phantom power simply because they aren't expected to do anything in standby mode: They're either on or they're off. The tradeoff is that these older appliances are much less energy efficient when they're running.

Of course, you can't always predict the phantom energy consumption of an appliance just by looking. Some devices that appear dark and cold might actually be drawing a current, and many newer TVs and electronics draw less than 1 watt when they're turned off, thanks to recent manufacturer efforts to comply with Energy Star guidelines [source: Energy Star].

An inexpensive power meter such as the Kill-A-Watt electric usage monitor can help you figure out which of your appliances are sucking up the most juice when they should really be sound asleep, but do the savings you hope to gain by unplugging your gadgets offset the $25 cost of a usage monitor? Read on to find out.