There's a simple theory at the heart of The Eco Button, and it's this: there's nothing like a big green glowing button to remind you to wind down your PC when you're not working.

And it's right, too. How many of us leave our computers running for half an hour when we're on the phone, or when we nip out to lunch, without activating sleep mode? Granted, on early iterations of Windows heading into sleep mode was akin to switching the computer off entirely, so tricky was it to resurrect the operating system from its slumber. Yet for some years that's not been the case, but we still leave our computers running on full power whether we use them or not.

The Eco Button is designed to do battle with that, claiming to save us a bit of money and do some good for the environment in the process. Put simply, it's a big button that connects to a USB port and glows green. When you're not using your PC, just hit the button and sleep mode is activated. Then the power button on the PC should, in theory, bring it back to life.

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It's basically paying £15 to bring to your attention a feature that your PC already has built in, but as a psychological reminder it has merit. It's also as simple as you'd need it to be: when you press the button it actually runs a small macro, that amounts to Start ... Run, and then typing in the name of the Eco Button executable. This then hibernates your machine.

There are, however, one or two flies in the ointment. Firstly, when you get the product, you're informed that you have to go to a website to download the software for it. Hmm. So off we toddled, figuring at least it was keeping the cost of packaging down, but we were then told that we couldn't have the software unless we tapped in our e-mail address. Why? When did this become a requirement to get the software promised on the packaging?

Still, the site accepted a nonsense e-mail address easily enough, and we got our software (after accepting a very long licence agreement). An interesting program it was, too, given that it outlined just how much money the Eco Button was potentially saving us, and brought to our attention the estimated running costs of the computer in front of us.

The other downside is the price for what's effectively a big green glowing button, which is quite a lot for what it actually is. It also flashes for some reason, which we found a little irritating, and we couldn't find a way to control its urge to emit a green light. You also, of course, need to make sure that sleep mode is supported on your system.

In principle the Eco Button is a fine idea, and it certainly has its value in reminding you to power down your machine when it's not being used. But it's arguably at the wrong price and just a little too brazen in its appearance to make it something you'd consider rolling out widely enough to make its aims of saving lots of power come true. But if you need the odd prompt, and don't mind having a beacon of greenness sat in front of you to serve that purpose, then it should, over a long period of time, repay your investment.

A nice idea, if a little too expensive for what it actually is. The fact that you seemingly can't disable the flashing of the button itself doesn't help, either.