{
  "registry": "KnowYourPrime Evidence Registry",
  "license": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Credit KnowYourPrime and link to the finding URL."
  },
  "fields": {
    "devices": "Devices this finding names, including models it says it does not cover. What was actually tested is in scope.applies_to; exclusions are in scope.does_not_cover.",
    "evidence": "Studies by role: anchor (the rating rests on it), conflicting, null_result, supporting.",
    "industry_ties": "Device-maker ties listed in Europe PMC metadata: author_affiliations names makers an author lists as an affiliation, funders names makers listed as funding. stated_ties holds ties a paper states only in its own conflict, funding or acknowledgement text, each read from that statement and worded to say only what it says. Sources are Europe PMC metadata, funding printed in the abstract, and those reviewed statements. An empty list means no tie was found there, not that the study is independent: many papers have no open full text to read. Metadata, not a judgment of the study. checked false means no Europe PMC metadata was available."
  },
  "id": "KYP-ER-0016",
  "version": "1.0",
  "reviewed": "2026-10-24",
  "url": "https://knowyourprime.com/evidence-wearable-sleep-stage-accuracy",
  "title": "Wearable Sleep Stage Accuracy",
  "question": "Can a smartwatch or ring tell which sleep stage you are in, compared with a sleep lab?",
  "measurement": "Sleep",
  "devices": [
    "Apple Watch",
    "Garmin",
    "Polar",
    "Oura",
    "WHOOP",
    "Fitbit"
  ],
  "rating": {
    "label": "Uncertain",
    "code": "uncertain",
    "definition": "Evidence is conflicting, inconsistent, or difficult to interpret.",
    "rule_version": "1.6",
    "rule_reasons": [
      "An anchor study was assessed but its own reported finding supports this claim only weakly, so the evidence is treated as unsettled rather than affirming.",
      "An anchor study was assessed but its own reported finding supports this claim only weakly, so the evidence is treated as unsettled rather than affirming.",
      "An anchor study was assessed but its own reported finding runs contrary to this claim, so the evidence is treated as unsettled rather than affirming."
    ]
  },
  "conclusion": "Only partly. Wearables tell sleep from wake well but name the stage correctly only around half to two thirds of the time, and REM is often the stage they miss most. Six current devices tested side by side all needed improvement for staging.",
  "reasoning": [
    "Sleep staging in a lab comes from brain waves, which no wrist or ring sensor records; a wearable infers stages from movement and heart signals. The three anchor studies, two systematic reviews and a six-device lab comparison, all found real but partial ability and none cleanly affirms accurate staging, so the rule rates the claim Uncertain."
  ],
  "key_results": [
    {
      "text": "In 53 healthy adults over one lab night, Apple Watch S6, Garmin Forerunner 245, Polar Vantage V, Oura Gen 2, WHOOP 3.0 and Somfit agreed with polysomnography on sleep stage 50 to 65 percent of the time (Cohen’s kappa 0.20 to 0.52), and the authors concluded all six needed improvement for staging.",
      "source": "doi:10.3390/s22166317",
      "source_url": "https://doi.org/10.3390/s22166317",
      "source_citation": "Miller et al., Sensors, 2022"
    },
    {
      "text": "Across eight studies of Fitbit Charge 4, Garmin Vivosmart 4 and WHOOP, WHOOP came within 1.4 minutes of total sleep and 9.3 minutes of deep sleep but differed by 21.0 minutes on REM.",
      "source": "doi:10.2196/52192",
      "source_url": "https://doi.org/10.2196/52192",
      "source_citation": "Schyvens et al., JMIR mHealth and uHealth, 2024"
    },
    {
      "text": "A systematic review of eight actigraphy studies found some ability to classify sleep stages, with methods too varied to pool.",
      "source": "doi:10.1111/jsr.14143",
      "source_url": "https://doi.org/10.1111/jsr.14143",
      "source_citation": "Yuan et al., Journal of Sleep Research, 2024"
    }
  ],
  "scope": {
    "applies_to": "Light, deep and REM sleep stages from consumer wrist and ring wearables compared with polysomnography in healthy adults.",
    "does_not_cover": "Total sleep time and sleep versus wake, covered in a separate finding; sleep disorder diagnosis; newer models released after these tests."
  },
  "limitations": [
    "Most tests are single lab nights in healthy adults.",
    "Stage definitions and agreement metrics differ across studies."
  ],
  "evidence": {
    "anchor": [
      {
        "key": "doi:10.1111/jsr.14143",
        "title": "A systematic review of the performance of actigraphy in measuring sleep stages.",
        "first_author": "Yuan",
        "journal": "Journal of sleep research",
        "year": 2024,
        "url": "https://doi.org/10.1111/jsr.14143",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.2196/52192",
        "title": "Accuracy of Fitbit Charge 4, Garmin Vivosmart 4, and WHOOP Versus Polysomnography: Systematic Review.",
        "first_author": "Schyvens",
        "journal": "JMIR mHealth and uHealth",
        "year": 2024,
        "url": "https://doi.org/10.2196/52192",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.3390/s22166317",
        "title": "A Validation of Six Wearable Devices for Estimating Sleep, Heart Rate and Heart Rate Variability in Healthy Adults",
        "first_author": "Dean J. Miller",
        "journal": "Sensors",
        "year": 2022,
        "url": "https://doi.org/10.3390/s22166317",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": [
            "conflict statement: the authors' lab receives funding and equipment from WHOOP"
          ]
        }
      }
    ],
    "supporting": [
      {
        "key": "doi:10.1007/s40279-024-02077-2",
        "title": "Keeping Pace with Wearables: A Living Umbrella Review of Systematic Reviews Evaluating the Accuracy of Consumer Wearable Technologies in Health Measurement.",
        "first_author": "Doherty",
        "journal": "Sports medicine (Auckland, N.Z.)",
        "year": 2024,
        "url": "https://doi.org/10.1007/s40279-024-02077-2",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ]
  },
  "evidence_last_evaluated": "Oct 17, 2026",
  "rating_history": [
    {
      "date": "2026-09-29",
      "rating": "Uncertain",
      "from": null,
      "rule_version": "1.6"
    }
  ],
  "versions": [
    {
      "version": "1.0",
      "date": "2026-10-24",
      "rating": "Uncertain",
      "change": "First published."
    }
  ],
  "research_desk": "https://knowyourprime.com/research-desk-sleep#stage_accuracy",
  "related_findings": [
    "https://knowyourprime.com/evidence-wearable-sleep-tracking-accuracy",
    "https://knowyourprime.com/evidence-under-mattress-sleep-sensor-accuracy"
  ],
  "related_articles": [
    "https://knowyourprime.com/how-wearables-track-sleep-stages",
    "https://knowyourprime.com/most-accurate-sleep-tracker"
  ],
  "methodology": "https://knowyourprime.com/methodology",
  "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0016, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-wearable-sleep-stage-accuracy"
}