But then looking about I read this "bought one of these a week ago and am using it with cheap recahrgeable cells, so battery waste will not be an issue. Unfortunately it reads alarmingly high, because it cannot take account of the non unity power factor in many home appliances, particularly fridge motors, compact fluorescent lamps and most home elctronics. As an electonics engineer I can understand why (you would need to sample the mains voltage as well as current, so it would not be easy for home users to install) but it negates its claims to give you proper power consumption and carbon output. It also has appalling resolution (the steps are around 17VA), so is hopeless at measuring anything much less than kettles, fires etc. " (http://www.bettergeneration.co.uk/ideas-for-saving-energy/the-efergy-energy-saving-meter.html)
So now I just don't know.