At this week's DEMO conference in California, sample devices from Green Plug ran off USB cables that can carry data as well as power, and they plugged into a transformer that looked more like a USB hub. Along with saving space, the technology could save some electricity. When the battery of a Green Plug device is full, it tells the charger not to send it any more juice. (Nokia is using similar technology on some of its cellphones.) Plus, fewer wall warts means fewer wasted watts. Even the smallest, most efficient transformers draw at least 0.3 watts just by being plugged in. If you replace, say, three chargers with one Green Plug hub, you've cut the waste by two-thirds.