I'm not into watches or wristbands, but for the last few weeks I've been wearing a fitness tracker on my finger. It knows how long I sleep and detects when I walk or run, and all I've gotta do is wear it like jewellery and forget about it.

However you get your workouts in, you might eventually reach a point where you want to keep track of them so you know how many calories you burn, what distances you travel, and what heart rate you hit while exercising. All of which is very easy to keep tabs on if you own an Apple Watch.

We're in a golden age of arguably unnecessary health gadgets, including several new entries to the market that aim to optimise our sleep, or at least give us lots of data describing it. We asked a few sleep experts what's useful and what isn't. Here are the features they liked.

Sleep is as important to health as diet and exercise and, thanks to new technology, tracking sleep is now routine in monitoring overall well-being. But are the devices used to do this actually useful, or have we simply found a more sophisticated way to clock watch?