There are roughly 160 million set-top boxes in homes around the U.S. – that's more than 80 percent of the country's domiciles. And every last one of them is a vampire. Set-top box

Not the Bela Lugosi or Robert Pattinson kind, of course – but the kind that suck power from your walls and money from your wallet.

The Natural Resources Defense Council has done a study on the energy usage of set-top boxes and found that they're responsible for $3 billion in annual power costs – with $2 billion of that occurring when they're not being used.

STBs with DVRs, in fact, use 40 percent more energy per year than non-DVR boxes, according to the study. Either way, it's a staggering number.

"The electricity required to operate all U.S. boxes is equal to the annual household electricity consumption of the entire state of Maryland," says the group.

On the upside, the industry's players are already redesigning set-top boxes to be more efficient – and energy consumption levels are expected to fall from 30 to 50 percent by 2020.

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