Saving energy has two good purposes: not only does it reduce the amount of carbon dioxide emited from power stations, but it also saves you money.

To do the job properly, though, you need to know how much energy each appliance in your home uses, which is a job for which Wattson is designed.

Wattson is a smart energy meter, with some useful extra features that separate it from most of the competition.

There are three main components: a sensor that clamps around one of the mains electricity cables coming into your domestic meter, a transmitter that attaches to the sensor and a display unit to be positioned anywhere within transmission range.

With its retro white and black acrylic case, the display unit has a faint hint of the kind of box electronics hobbyists used to use for home-grown projects, which adds a nostalgic touch to the product.

There's no obvious display or meter on the box. Instead, a row of five pink digits (which can show letters and numbers) is displayed through the Wattson's white acrylic top, showing either the current power use in watts or kilowatts or, with a quick flick of the unit, your electricity costs for the year if you were to continue running the home with exactly the same energy use. This is unlikely - energy use changes with days and with seasons - so the cost display is not hugely useful.

A bank of red and blue lights underneath the display also changes colour, depending on the power consumption. From blue to purple to red, you can see at a glance how energy hungry your home is.

The display unit uses rechargeable batteries so it can be carried around the house, and so it's possible to unplug appliances in turn to check how the energy use changes as different things are in use. It can also be connected to a PC using the supplied USB cable and by downloading the Holmes software (see the name connection?) from the DIY Kyoto website, you can plot energy use over days, weeks or months to make a graph of savings. The main problems is that you'll need to like the look of Wattson as a design installation as well as an energy meter to justify its relatively high price.

Vista compatible: Yes