Kettle

Kettles use an extraordinary amount of electricity. I saw a review of one of those machines you can buy which measures in real time your electricity consumption in your house, and the reviewer said when he boiled his kettle the machine showed such a massive spike in energy usage, it made him totally conscious of only putting into the kettle as much water as he actually needed for his cup of tea.

Which ties in neatly with the UK's National Grid having up-to-the-second information on what was on telly, so that for instance during the commercial break in an episode of Coronation Street they could quickly switch on a whole extra nuclear power station, to cover the nation's kettles being switched on. Mad but true!