Garmin Swim: pool shark

    It's a classic mistake: you plan to do a couple of lengths of your local pool, but you keep losing count and starting again until, by the time you towel off, it's a decade since you entered the pool and you've exercised yourself into a giant scaly man-shark. Next time, let this watch do the counting — and the timing, and graphing of your performance. It'll even tell you what stroke you were doing at the time, and clean your new gills.
£130, garmin.com