A force as insidious as Dracula is quietly sucking a nickel of every dollar’s worth of the electricity that seeps from your home’s outlets. Allow your computer to hide in the cloak of darkness known as “standby mode” rather than shutting it off: That’s vampire electronics.

The latest estimates show 5 percent of electricity used in the United States goes to standby power, a phenomenon energy efficiency experts find all the more terrifying as energy prices rise and the planet warms. That amounts to about $4 billion a year. The percentage could rise to 20 percent by 2010, according to the U.S. Department of Energy.