Your wearable is lying to you about sleep

What you should do about it

Victor Rotariu
3 min readAug 2, 2022


Bad sleep kills

Sleep is the most important element for your health, arguably more important than nutrition or exercise. There are over 260,000 scientific studies on sleep on PubMed. What they find is simple: disrupted sleep kills you, makes you unhappy and unproductive. Everything is worse from bad sleep.

The average person lives 10 years less due to bad sleep.*

Good sleep is not just sleep duration, although the volume itself is a huge problem. Good sleep is also about proper sleep architecture. This is a fancy way of saying you need to have good quality for each of the sleep stages: stage 1, 2, and especially deep sleep and REM sleep.

How much deep sleep did you get last night? What about REM sleep?

If you have a wearable, such as an Apple Watch, a fitness band, an Oura ring or a sport watch, you will be looking at it now. It will tell you that you got X minutes of deep sleep and Y minutes of REM sleep.

Your wearable is lying to you.

It cannot measure your sleep stages.

Although companies make big claims about sleep stages, they don’t offer any actual proof that their product are tracking these. However, there have been scientific studies evaluating their accuracy on sleep.

This study found the Oura ring had an agreement of 51%-65% in detecting the sleep stage. So it was right in identifying the sleep stage about half the time. That is as good as if you were to throw a coin to guess which sleep stage you were in.

It’s not just Oura. All current wearable have similar or worse precision for measuring sleep stages, as seen in all the studies that evaluate this: 1, 2, 3, 4, 5, 6, 7, 8, 9.

As one study author puts it: “High variability in sleep stage-tracking performance suggests that these devices, in their current form, are still best utilized for tracking sleep-wake outcomes and not sleep stages.”

If you don’t have the patience to read scientific studies, there is also a scientist on YouTube (Quantified Scientist) who tests wearables versus…



Victor Rotariu

Polymath. Curious. Writing a book on how to create an ideal life for our Paleolithic mind and body