Millions of people around the world rely on their smartwatches to track their calories, sleep hours and workout stats, but new data has raised concerns.

Reports indicate that smartwatches don't measure most of these metrics directly, with many common metrics just being estimates.

Body Torque Personal Training founder Alex Flint says things like calories burned, fitness scores, and hours slept aren't accurately tracked.

"I use it as an overall guide, I think probably the best thing that I would use it for is just to see how I feel - compared to what my watch is telling me."

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