Griffin's £18 AirCurve iPhone speaker is a refreshing piece of technology: it never needs charging, updating or rebooting.

It's a transparent block of silicone polycarbonate with a groove - a coiled waveform horn - running through it that causes it to resonate and amplify whatever's playing on your iPhone. It's fair to say that when we were shown a prototype version back in the summer, we were smitten. Now we've got one in to test, we're every bit as taken with it.

The AirCurve can't, of course, crank up the volume very high. It's not much more than 10cm long and there's a limited amount of resonance that can build up, so it can only add about 10 decibels to the overall volume. This means it's ideal if you want something to listen to while you're sat typing an essay or report or engaged in another activity that repays a bit of aural distraction on the side.

The AirCurve is designed to work with the iPhone 3G, but comes with an adapter (a small white plastic tray) that sits under a iPod touch and keeps its slimmer dimensions in check. Should you wish, you can use the connection cable supplied with your iPhone and use the AirCurve as a dock so the handset charges while in use.

At only £18 with no maintenance or running costs and a fantastic curiosity factor, the Griffin AirCurve is the sort of 'green' gadget that's actually rather cool.

Griffin AirCurve ambient iPhone speaker