For a tracker you never have to take off, try the Garmin Vivofit (£70). Its battery lasts for over a year and is waterproof, meaning you can keep it on while you take a shower. The Vivofit tracks steps, distance, calories, and sleep and can also track workout details when paired with a heart-rate monitor (sold separately). An activity bar will show you whether you've been sitting for too long. The Vivofit syncs wirelessly with its free iOS or Android app as well as your computer.