Fitbit
Fitbit Charge 6 validation studies
7 peer-reviewed studies in the CircaTest corpus that validated this device against polysomnography or another reference standard.
Read CircaTest's Fitbit Charge 6 review →Performance evaluation of consumer sleep-tracking wearables and nearables in healthy young and older adults
Searles et al., 2026 · Sleep Advances
First peer-reviewed paper to specifically benchmark consumer sleep-tracking devices against PSG in older adults (age 56-80) versus young adults (19-24). Critical because nearly every other study in the corpus is in young or middle-aged adults. The headline finding is that bias and limits of agreement are larger in older adults across all four tested devices, meaning the accuracy figures CircaTest cites for younger populations should not be directly extrapolated to readers in their 60s+. Also tests Withings Sleep Mat and Sleep Score Max (the nearable category), which CircaTest is in the process of adding to its catalog.
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.
A performance validation of six commercial wrist-worn wearable sleep-tracking devices for sleep stage scoring compared to polysomnography
Schyvens et al., 2025 · Sleep Advances
Single most editorially important study in the CircaTest corpus. Six commercial wearables tested against PSG in a uniform protocol means the kappa values are directly comparable in a way most validation studies are not. Drives the head-to-head accuracy figures across CircaTest's comparison content. Limitations: tested previous-generation models (Series 8 not 10, Charge 5 not 6, original ScanWatch not 2) so the results are upper bounds for current models, not direct evidence.
Performance of seven consumer sleep-tracking devices compared with polysomnography
Chinoy et al., 2021 · Sleep
A 7-device same-protocol comparison from the US Naval Health Research Center. Comparable in spirit to Schyvens 2025 but earlier (2021), with different device set including Garmin Fenix 5S and Garmin Vivosmart 3. Useful editorial counterweight to Schyvens for cross-validation: the Garmin underperformance shows up in both studies.
Accuracy of Wristband Fitbit Models in Assessing Sleep: Systematic Review and Meta-Analysis
Haghayegh et al., 2019 · Journal of Medical Internet Research
The most-cited meta-analysis of Fitbit accuracy. CircaTest references the 81-91% sleep/wake accuracy figure as the editorial baseline for any Fitbit claim, particularly because no peer-reviewed Charge 6 specific validation has been published. The very low specificity range (10-52%) on early models is the source of the well-known 'Fitbits overestimate sleep' criticism.
A validation study of Fitbit Charge 2 compared with polysomnography in adults
de Zambotti et al., 2018 · Chronobiology International
First peer-reviewed PSG validation of a Fitbit model with sleep staging (the Charge 2 was the first staging-capable Fitbit). Establishes the per-stage accuracy figures (light 81%, deep 49%, REM 74%) that CircaTest's sleep-tracker-accuracy-explained guide uses to show that 'sleep score' aggregates can hide major per-stage variation.
How well does a commercially available wearable device measure sleep in young athletes?
Sargent et al., 2018 · Chronobiology International
Important athlete-population validation. The 52-minute mean overestimation with ±152 min SD shows just how variable Fitbit overestimation can be on a per-night basis, which CircaTest's accuracy guide uses to discourage over-interpretation of single-night sleep scores from any wrist-worn device.