06/11/2026
Your sleep tracker may be wrong about REM.
Not because it is useless.
Because it is estimating.
Polysomnography, the gold standard sleep study, reads brain waves directly. That is how sleep stages are actually measured: REM, deep, light, and awake.
Your Oura, Whoop, Apple Watch, Eight Sleep, and other wearables are reading signals like heart rate variability, movement, breathing, skin temperature, and restlessness.
Then an algorithm makes its best guess.
So when your tracker says you got 47 minutes of REM, remember: that number is an estimate, not a verdict.
What matters more:
· Your trends over time
· How often you wake up
· Whether your sleep feels fragmented
· How you feel in the morning
· Whether your body is fighting heat overnight
Wearables can be helpful.
Not as a judge.
As a pattern detector.
Use the trend, not the score.