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What levels of sleep do devices such as AURA, WHOOP, FitBit, and Apple Watch detect?

#58 – AMA with sleep expert, Matthew Walker, Ph.D.: Strategies for sleeping more, sleeping better, and avoiding things that are disrupting sleep

June 18

The devices are good at estimating duration of sleep, but not the stage of sleep. They are good at detecting the two class algorithm-- total sleep time, awake or asleep. They fail at detecting the four class model-- whether someone is awake, in light or deep non-REM sleep, or in REM sleep.