Meta-analysisvs PSG2025
Performance of consumer wrist-worn sleep tracking devices compared to polysomnography: a meta-analysis
Lee et al., 2025 · Journal of Clinical Sleep Medicine
The most comprehensive recent meta-analysis of consumer wrist-worn sleep trackers vs PSG: 24 studies, 798 patients, 12 different brands including Fitbit, WHOOP, Garmin, Apple Watch, Empatica E4, and Xiaomi Mi Band 5. Headline finding is that across the entire device set, consumer wrist trackers UNDERESTIMATE total sleep time by ~17 minutes (95% CI -26 to -7) and UNDERESTIMATE sleep efficiency by ~4.7 percentage points, both statistically significant. This is the strongest published quantitative answer to the question 'how wrong are consumer trackers on average' across the wrist-worn category. Important limit: pooled across brands, no per-device breakdown extracted into this record.
Apple Watch (multiple generations across included studies)Fitbit (multiple models across included studies)WHOOP strap (multiple generations across included studies)Garmin (multiple generations across included studies)Xiaomi Mi Band 5