An estimated 13 percent of household electricity use, according to a recent study published by the California Energy Commission, is from appliances in low-power mode (which is to say, not performing any of their primary functions). 

Standby mode, the least amount of energy an appliance can use without powering down, is just one example. Many appliances have multiple low-power modes.

A DVD player, for instance, may have both a standby and sleep mode. Computers, as well, often save power by shutting down one or more components without turning completely off. 

What it costs
The costs of these low-power modes are enormous. Standby power alone accounts for 5 of that 13 percent of household electricity use. 

In 2000, a group of researchers from Lawrence Berkeley National Laboratory estimated that each year Americans spend about $4 billion just on standby power. 

Generating that electricity puts roughly 27 million tons of CO2-equivalent emissions into the atmosphere (more than 3.7 million cars' worth) every year.

While the amount of low-power mode energy required by most new appliances is going down, the number of appliances (from washing machines to air conditioners) with continual power needs is increasingeclipsing those savings. The U.S. Department of Energy estimates that standby power could consume as much as 20 percent of household electricity by 2010.

Further losses
Worse yet, some of our electronics never go into low-power mode because they're hooked to networks that require constant feedback. Most desktop computers are left on all the time for just this reasondrawing (on average) a steady 70-watt current. The monitor may be off, but the processor, fan, and other hardware may still be running. 

Your cable box, too, is perpetually drawing current as it talks to the network. Have an Internet phone? That, as well, is always on, ready to take a message.

Energy-efficiency experts are busy identifying ways that manufacturers can reduce the amount of energy required to maintain a network presence, hold a channel, or answer the phone when you're not there. Some promising work can be found here. 

Why we don't sacrifice convenience?
If the net impact of all our leaky appliances is so huge, why aren't we compelled to change our habitsor do without a little convenience? 

A colleague of mine here at Rocky Mountain Institute shares a useful anecdote. His home A/V system (TV, cable box, DVD player) and communications system (cable modem, WiFi router, Internet phone, and cordless phone with answering machine) uses about 45 watts of electricity continuously. 

Even though he'd like to save that energy, he leaves the system on all the time. If he turns off the power bar that links everything to the wall, his phone won't take messages and he'll lose Internet connectivity. 

What's the cost of this convenience? He estimates about $40 dollars a year. 

What you can do
If you're looking to reduce your energy use and tread more lightly on the planet, changing your habits is a good starting point. 

• Shut your computer and printer down (all the way) when not in use. Some people find it useful to plug all their IT equipment into one power bar, then flip the switch once they've shut down. 

• If you have an A/V system that can be turned off entirely without sacrificing performance, do so. 

• Keep cell phone chargers out of the wall when you're not charging the phone. Those little power bricks often draw a little currenteven when you're phone's not connected. 

Making informed choices
Most importantly, educate yourself. The U.S. government's Energy Star program rates appliances and often has information about their standby (or low-power) mode energy use. For home electronics, low standby power use is a key criterion for qualifying products.  

In 2006 alone, the program saved some $14 billion on Americans' utility bills and helped avoid more than 35,000 megawatts of peak power demand (equivalent to the capacity of 70 new power plants). 

These small changes may not make a huge dent in your monthly electricity bill, but they can add up.