All things plugged in will bleed some energy. Called "standby" electricity loss because it's so often associated with electronics in standby or idle mode, it's also known as "phantom" or "vampire" electricity (for obvious reasons). Even turned off, many appliances keep drawing power. Same goes for all those chargers — whether or not a device is charging! That means the charger continues to use power even if your cell phone/portable vacuum/toothbrush/wireless drill isn't attached, let alone charging. Power supplies don't just convert energy; they consume it. Anything with a transformer — those black boxes on power cords — draws power as long as it's plugged in. And because of poor design, these boxes waste up to three-fourths of the electricity that passes through them.

The Natural Resources Defense Council says the cost of plugged-in but not used devices is about $165 per household, or $19 billion across the U.S. That amounts to about 44 million tons of carbon dioxide, or 4.6% of the country’s total residential electricity generation, points out The New York Times.

Unplug 10 of those black box transformers and you save, depending on how much you pay for electricity, $20 a year. But add up the energy used when we are not using our TVs, stereos, cable boxes (all turned "off" but really in standby mode), computers, modems, routers, printers (these networks tend to be left on all the time), rechargeable devices (cellphones, computers, MP3s, cameras, wireless tools and vacuums, toys, cordless phones) and their transformers, and you get the equivalent of a year's output of 17 power plants. The oft-cited research by Alan Meier of the Lawrence Berkeley National Laboratory finds that vampire energy accounts for about 5% of all residential electricity use.

The Department of Energy sets the loss at 5% to 8% of a single family home's annual usage, which is an entire month's energy bill. That's a national average; take a walk through your home and count the number of devices you have plugged in (don't forget the washing machine) and you may find that you're spending 25% of your energy bill to feed vampires.

Good to know:

computer and phone with plant and green battery If you're not using your computer, unplug it or at least turn off the monitor. And plug your phone into a power strip. (Photo: David M G/Shutterstock)

  • Use power strips: Instead of unplugging things one at a time, make the job easier with power strips. You can then switch off or unplug the strip to turn all the devices off at once — really, truly, actually off. There are all kinds of "smart" power strips on the market that make the task ever easier: strips with motion sensors (leave the house/office and it'll shut off all devices automatically); strips that have a few "always on" sockets, with the rest turned off as you please; and power strips that allow a master device to control the power use of its paraphernalia (turn on/off your computer or TV or stereo, and the peripherals are turned on/off too). In the meantime, I'm going to put my surge protectors on timers because, well, I don’t always remember to switch them off. OK, that's almost never remember, and at least this way they'll be off when I'm most likely to be sleeping.
  • Your screen will be fine; save energy instead: Screen savers don't save energy. If you won't be using your computer and don't want to shut it down (but why?), turn off your monitor. I've read that we spend as much as $100 a year running screen savers. Along the same lines, you can reduce the energy consumption of your TVs and computers by dimming the screen: Reduce the brightness by half, and you can cut energy use by 30%.
  • Check yourself: Measure the electricity usage of all your appliances — on or off — and see for yourself which ones are the big suckers. A popular power monitors is Kill A Watt.
  • Standby is better than on: Whether you consider vampires a threat or not, it's when things are turned on that they're consuming the most power, so turn them off even if you don't unplug!

Editor's note: This story has been updated with new information since it was published in December 2008.

Should I unplug my appliances and, if so, will I save money on my electric bill?
Appliances -- also known as energy vampires -- keep drawing power even when they're off.