I like those strangely boxy little electric cars. I like the message of their looks. They defy the traditional sleekness of car design and instead make a point of their functionalism. They say “OK—we may look a bit funny but we use a third of the energy your car is using.” They advertise their owners’ rethought priorities. They’re nearly as cool as bikes.

On the same spectrum are two small items of recent domestic technology. The first is a little box with a screen which shows, in watts, how much electricity you’re using. Switch on a light, and the figure goes up by 60 watts. Turn on the kettle and it goes up by another 3,000. Within hours of installing this box—which takes a couple of minutes—your energy usage changes. I discovered I’d been drawing a constant 140 watts for the last 15 years—for nothing (a defunct alarm system hidden