They are relied upon by fitness fanatics to record all manner of data from their length of runs to heart rate, pace and even changes in elevation during a jog.
But one thing smartwatches shouldn't be relied upon when exercising is counting calories, scientists claim.
Academics said the devices are not accurate at working out how many units of energy have been lost during exercise.
In fact, researcher Dr Cailbhe Doherty claimed there is a 'high degree of error' in the methods used.
This means that watches may tell users they have burnt 1,000 calories - when they have actually only burnt 300.
