Apple’s own intro text to sleep stages mentions brain waves to gather this data. How then are they able to know this just from heart beats and an oximeter?
Ask HN: How do smart watches track sleep stages?
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Re: Ask HN: How do smart watches track sleep stages?
#2Simpler ones just use body movements as a proxy for sleep phases. Since sleep phases are linked to different activity levels, trackers can use anything that indicates (lack of) activity to guess at phases happening. It doesn't necessarily work all that well though.
Re: Ask HN: How do smart watches track sleep stages?
#3> How do smart watches track sleep stages?
As an insomniac with sleep maintenance issues: poorly. When I wore it, it thought i was sleeping regular hours.