Household gadgets and appliances suck power even when they’re shut off, constituting 10 percent of the electricity use in the average San Francisco Bay area household and costing residents about $80 a year, according to a new study by researchers at the Lawrence Berkeley National Laboratory. These so-called vampires include everything from stereos and computers to bread machines and microwaves. Studies in Germany, Japan, and the Netherlands have also found that appliances and other equipment that drain standby power from the grid account for as much as 10 percent of residential electricity consumption. An easy solution is to unplug the machines when they’re not in use. Another is to convince manufacturers to use more efficient technology that will cut down on standby energy use.