Picked a couple of these “Ecowatt” devices up while in Tokyo, from Bic Camera. They monitor power consumption of whatever you’ve plugged into it. Here I had my MacBook Pro plugged in and running (no sleep) for about 24 hours. The device simply runs through four measurements — two I have no idea about because the symbols are in Kanji, and then two more that are kilowatt hours of consumption and estimated CO2 that would be exhausted from, presumably, a power plant that produced CO2 gas.
There’s lots of work to be done around this sort of idea, first of all a more compelling UI. Maybe even the draconian edition that starts to dim your display or attenuate your Internet as you run past your daily quota of energy.