How To Get Sleep Stages From Your Apple Watch

Your Apple Watch can accurately track sleep and wake, but unfortunately it doesn’t have an algorithm for measuring your sleep stages and other aspects of your sleep quality.

SleepSpace turns your Apple Watch into a high resolution sleep tracker by activating the workout mode of your watch. This turns on the photoplethysmography (PPG) sensor continuously, which the Apple Watch uses to measure your heart. This will drain your Apple Watch at night so make sure you charge the watch before you go to bed in order to get your full night of data.

You can see in SleepSpace the app changing heart rate every 5 seconds, whereas Apple typically measures heart rate every 5 minutes. Measuring your heart every 5 minutes is not frequent enough to measure things like Rapid Eye Movement (REM) sleep, deep sleep, and cortical arousals (i.e. brain awakenings at night). By turning on the PPG sensor continuously SleepSpace is able to measure these nuances of your sleep.

You can see the PPG sensor is activated when you are wearing your Apple Watch by lifting it up slightly. When you lift it up you should see a green light that is always on. This means your heart rate is being measured at a higher frequency and your sleep quality can be accurately determined.

Dr. Daniel Gartenberg demos the green light PPG sensor in this video and gives you other tips on how to interpret your sleep quality.