None of the popular wrist-based trackers have an oximeter. You need red and infrared light for that, and it is really tricky to get accurate measurements at the

None of the popular wrist-based trackers have an oximeter. You need red and infrared light for that, and it is really tricky to get accurate measurements at the wrist in any case. You don't measure respiration rate with oximetry in any case, oxygen saturation does not change that fast. The more advanced solutions are mostly based on Heart Rate Variability which shows some correlation to sleep stages. Source: also worked on this.