Did Your Smartwatch Tell You Your "Recovery Score" Is 42% Today? Why Sleep Doctors Say Wrist Sensors Are Giving Healthy People Insomnia
We compared wrist photoplethysmography (PPG) validation studies against hospital ECG and sleep-lab polysomnography (PMID 32345045) to show you what your watch gets right (resting heart rate) and what it guesses wrong (deep sleep minutes and daytime HRV).
In head-to-head sleep lab validation studies published in Sleep (PMID 32345045), researchers hooked adults up to gold-standard polysomnography (scalp EEG wires that directly measure brain waves, eye movements, and muscle tone) while they wore leading consumer smartwatches on their wrists . The verdict: wrist wearables are very good (~88%–93% accurate) at telling when you fell asleep and when you woke up, and 97%+ accurate at measuring overnight Resting Heart Rate (RHR) . However, because a watch on your wrist cannot read brain waves, its guesses at "Deep Sleep vs. Light Sleep vs. REM" disagreed with hospital EEG brain-wave recordings 30% to 45% of the time !