Yesterday this little gizmo came in the post from British Gas - a free live updating electricity usage meter. After wrapping a sensor around the mains feed and pairing it with the display, it keeps track of your usage day-by-day, and shows a whole bunch of nerdy stats.

Seems to work pretty well, and it's crazy seeing the numbers jump up and down when you switch TV's on etc.

What surprised me though is that my iMac, Drobo (with 4 hard drives whirring), and another external hard drive, only consumes about 80 watts average, which is pretty good really.