Apple Watch Series 7, Fitbit Charge 5, and Polar Vantage M2 demonstrated parameter-specific bias and limited agreement with PSG and actigraphy, suggesting these devices may be appropriate for longitudinal self-monitoring rather than clinical-grade assessment of sleep architecture.
Fitbit Charge 5 significantly overestimated light sleep compared with PSG.
Apple Watch Series 7 significantly underestimated light sleep and overestimated REM sleep compared with PSG.
Polar Vantage M2 showed a significant positive REM bias compared with PSG but no significant differences for other sleep parameters.
Agreement between all three consumer wearables and PSG was generally weak with wide limits of agreement across sleep parameters.
The study was a prospective observational design conducted in healthy adults aged 18–45 years with concurrent home PSG and actigraphy as reference standards.
Consumer sleep-tracking devices were deemed more appropriate for longitudinal self-monitoring than for clinical-grade assessment of sleep architecture.
This research suggests that three popular consumer wearables — the Apple Watch Series 7, Fitbit Charge 5, and Polar Vantage M2 — do not accurately measure sleep stages when compared against the medical gold standard (polysomnography, or PSG) and a research-grade activity monitor. Specifically, Fitbit tended to overestimate light sleep by nearly an hour, Apple Watch underestimated light sleep and overestimated REM sleep, and Polar overestimated REM sleep. The agreement between all devices and PSG was generally weak, meaning the numbers these gadgets report can differ substantially from what clinical sleep testing would show. The study involved 54 healthy adults aged 18 to 45 who wore one of the three devices alongside a professional actigraphy monitor while also undergoing home sleep testing. Researchers used standard statistical methods (Bland-Altman plots and intraclass correlation coefficients) to measure both the size and consistency of the differences between devices and PSG. Among the three, Apple Watch performed best overall, followed by Fitbit and then Polar, though none performed well enough to be considered clinically reliable for measuring sleep architecture. This research suggests that while these wearables may be useful for tracking general sleep patterns and trends over time, they should not be relied upon for diagnosing sleep disorders or making clinical decisions about sleep health. The specific biases each device shows — such as overestimating certain sleep stages — mean that the sleep stage breakdowns they provide can be misleading when compared to what a sleep specialist would measure in a clinical setting.
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Upload Your LabsAlhejaili F, Alshumrani R, Alamoudi W, Wali S, Bamagoos A, Wazira L, et al.. (2026). Performance of three consumer sleep-tracking devices compared with Actigraphy and Polysomnography.. Sleep medicine. https://doi.org/10.1016/j.sleep.2026.109059