I actually wrote about this not too long ago. As after 7 years of loving my smartwatch I decided to stop wearing it everyday. There is a lot I liked about it, but upon researching more about them I learnt about the amount of radiation and EMF's they emmit.

I know EMF's are everwhere but having strapped straight to your skin is a whole other story that there is no long term data on.

So I now just use mine on longer training sessions and race days. But you are right, it's a technilogy that is certainly here to stay.