I'm not running Watch OS 9, still Watch OS 8. I did a run in the heat yesterday (30C) and for the entire run (aside from a brief ramp up) my heart rate was at the max (172bpm).
If I understand correctly, Watch OS 9 will allow me to set target heart rate zones? So if my target is 140bpm, what happens when I'm exceeding that? Is there a notification from the Watch?
And does this work on the SE?
I can’t speak for the SE, but I use the alerts on my series 7. It vibrates and gives an audio alert (optional) to let me know when I’m over or under the HR zone that I’ve set as my goal.