The problem is that to monitor your sleeping patterns, a valuable feature most of these new smartwatches support, the watch needs to be on your wrist. So leaving your watch charging overnight while you slumber isn’t going to work. But smartwatches have small batteries compared to smartphones, so should only take 2 - 4 hours to fully charge, depending on the model.
The company claims that the SpO2 monitor will help its devices look for signs of sleep apnea and other breathing problems, potentially great features for devices that are meant to be worn 24/7. It'll be used primarily in Fitbit's forthcoming Sleep Score Beta, which further analyzes sleep quality using heart rate and breathing data. Starting sometime this November, users with devices that only have heart rate monitors can get a "sleep score" after each night's sleep. Those with an Ionic, Versa, or Charge 3 will presumably have better data thanks to the SpO2 monitor collecting breathing data.
Most stores that sell these smart watches feature display models that you can pick up and touch. We recommend getting a feel for how these watches operate before you invest in one of your own. Specifically, you’ll want to know the form of navigation each of these use to go through the various screens, apps, and functionalities. We were partial to twistable bezels and dials, but you might be used to swiping your way through screens.
Samsung's Galaxy Watch, a Tizen OS watch (starting at $329), is our favorite smartwatch for Android users. In addition to up to four days of battery life and a great design, the Galaxy Watch offers built-in GPS, heart rate sensor, water-resistance, Samsung Pay support, plus a nifty rotating bezel for navigating the interface. You can also download music from Spotify to the watch for offline listening. However, you get far fewer apps than you would with a Wear OS watch.