Calorie counting by smartwatches

Hi all,

Do you know that smartwatches and smartphones tend to be off by about 40 to 80 percent when it comes to counting calories burned during an activity?

Have you experienced it?

I have. I have Garmin watch and when I tried to loose weight with 500kcal deficit according to my daily burn, I was actually gaining weight (and I don't mean muscles 🙃)

https://med.stanford.edu/news/all-news/2017/05/fitness-trackers-accurately-measure-heart-rate-but-not-calories-burned.html