My old Sony Smartwatch 2 connects via Bluetooth without any issues.
Pebble 2 is working.
All Pebbles work.. (I have a couple of the originals), my Garmin 235 works (and expect all the garmin too), and also every single android wear watch (I have the original Moto 360, but have tried newer ones too) works..
Literally everything except the Apple Watches and the Tizen Samsung's in fact.. It would be tricky to find a watch that isn't compatible!
Mi samsung Gear S3 es compatible con mi Nokia 8, aunque es complicado conectarlo la primera vez.
My Samsung Gear S3 is compatible with my Nokia 8, although it is difficult to connect it the first time.
I am using an LG G Watch R without any issues. Well, the latest Android Wear updates have hobbled the watch somewhat, but that's not the phone's fault...!