Smartwatches compatible with PC?

[Dracindo]

Can smartwatches also connect to your computer? I'm guessing that's what Twitch streamers and Youtube content creators use when they want to show their heart rate on their videos. If not, how do they do it?

And if so, what are the PC requirements to connect with your smartwatch? And on top of that: which one would you recommend me for the above explained situation? It may have more feats, but I don't wish to spend a lot on a smartwatch.