Most U.S. utilities are currently piloting time-specific pricing schemes like the one in Germany, and Wong hopes that this will create a new market for the Joule: helping residential and small commercial consumers track price shifts. Many utilities are planning to break their residential rates into just a few categories--a level of complexity the Joule could handle. Southern California Edison (SCE), for example, plans just three pricing categories: off peak, regular peak, and critical peak (the latter likely limited to the hottest summer afternoons, when the grid is most at risk).

Wong says that on such days, the Joule could make a major difference. "If one home turns off their air conditioner, that's one kilowatt. But if you get 1,000 homes, all of a sudden you're talking about one megawatt."

Ambient and ConsumerPowerline, however, will soon face competition thanks to new utility-installed meters that will use the cellular-telephone network and Wi-Fi, rather than satellites, to relay pricing information. SCE's $1.7 billion SmartConnect program, for example, aims to install smart meters in five million southern California homes and businesses between 2009 and 2012.

Paul De Martini, who directs the SmartConnect program, says that the meters will communicate with the utility via the cellular network, then broadcast pricing and local power-consumption information to home networks, probably using a low-power form of Wi-Fi called ZigBee. De Martini says that at least 20 companies, including giants such as General Electric, are developing ZigBee-enabled devices to pick up, interpret, and display that information. De Martini's team at SCE has assembled a device of its own: a battery-powered ZigBee refrigerator magnet with green, orange, and red LEDs that represent off-peak, normal-peak, and critical-peak pricing. A commercial version of such a device could be cheap enough to give away.

De Martini thinks that an even more effective means of encouraging conservation will be devices that display household power consumption in real time. "The thing that really works well for people is when they can see it dynamically, kind of like when you're at the gas pump and you can see how much it's costing you as the dial clicks around," he says. That dynamic view, he predicts, will not only shift consumption from peak to off peak, but it will actually reduce total power consumption.

Ambient and ConsumerPowerline may survive by incorporating ZigBee into their own devices. But Wong says that his company won't make that move unless this winter's pilot test proves that the Joule display motivates enough negawatts. "We know there will be a behavioral response," he says, "but we need to understand the full value of that behavioral response."