3 links have been added on this idea.
  1. Weird – this measures your sleeping patterns too. Want one!

  2. Done oura measures your heart rate https://www.wired.co.uk/article/oura-ring-uk-sleep-tracking#:~:text=The%20ring%2C%20which%20is%20designed,track%20day%2Dtime%20activity%20too.