{
  "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-0021",
  "version": "1.0",
  "reviewed": "2026-10-24",
  "url": "https://knowyourprime.com/evidence-cuffless-blood-pressure-at-night",
  "title": "Cuffless Blood Pressure Accuracy at Night",
  "question": "Can a cuffless smartwatch, bracelet or ring measure blood pressure accurately while you sleep?",
  "measurement": "Blood pressure",
  "devices": [
    "Aktiia (Hilo)",
    "Samsung Galaxy Watch",
    "Cuffless wearables"
  ],
  "rating": {
    "label": "Uncertain",
    "code": "uncertain",
    "definition": "Evidence is conflicting, inconsistent, or difficult to interpret.",
    "rule_version": "1.6",
    "rule_reasons": [
      "Anchor-grade evidence affirms the core relationship.",
      "Multiple supporting studies are consistent with the core relationship.",
      "An anchor study is present but its own reported finding does not cleanly affirm this claim, so it does not count toward the Established threshold.",
      "The claim rests on a single anchor whose finding affirms it; a second independent affirming anchor is needed to reach Established.",
      "A clean anchor supports this claim, but an unresolved conflicting study contradicts it on the core relationship, so the evidence is treated as in genuine dispute."
    ]
  },
  "conclusion": "Not yet. Across pooled studies, cuffless devices agreed with 24-hour cuff monitoring during the day but read significantly higher at night, and an Aktiia bracelet worn by 41 people read nighttime systolic pressure 15.5 mmHg higher than the cuff monitor, understating the normal overnight dip.",
  "reasoning": [
    "Nighttime blood pressure carries strong prognostic weight, and the overnight dip is one of the things a 24-hour cuff monitor exists to measure. A meta-analysis of cuffless devices against 24-hour monitoring found daytime agreement and significant nighttime differences, and concluded current devices are not reliable at night.",
    "One watch-like sensor study reported small nighttime differences and is the clean anchor, but two studies of the Aktiia bracelet found nighttime readings markedly higher than the cuff. The rule rates the claim Uncertain."
  ],
  "key_results": [
    {
      "text": "In a meta-analysis of studies from 2019 to 2024, cuffless devices differed from 24-hour ambulatory monitoring by -0.99 mmHg systolic in the daytime (95 percent CI -3.47 to 1.49) but by 4.48 mmHg systolic (0.27 to 8.69) and 5.64 mmHg diastolic (2.57 to 8.71) at night.",
      "source": "doi:10.1016/j.ajpc.2025.101342",
      "source_url": "https://doi.org/10.1016/j.ajpc.2025.101342",
      "source_citation": "Lee et al., American Journal of Preventive Cardiology, 2025"
    },
    {
      "text": "In 41 participants wearing the Aktiia bracelet for 6 to 12 days, nighttime systolic pressure averaged 15.5 mmHg higher than ambulatory monitoring (95 percent CI 11.8 to 19.1) and diastolic 11.8 mmHg higher, while daytime systolic was similar (1.0 mmHg).",
      "source": "doi:10.1097/hjh.0000000000003428",
      "source_url": "https://doi.org/10.1097/hjh.0000000000003428",
      "source_citation": "Tan et al., Journal of Hypertension, 2023"
    },
    {
      "text": "A watch-like optical sensor worn during conventional 24-hour monitoring showed small average nighttime differences, and its authors concluded cuffless 24-hour monitoring may become a clinical possibility.",
      "source": "doi:10.1038/s41598-023-33205-z",
      "source_url": "https://doi.org/10.1038/s41598-023-33205-z",
      "source_citation": "Proença et al., Scientific Reports, 2023"
    }
  ],
  "scope": {
    "applies_to": "Cuffless wearables that estimate blood pressure from optical or other signals, compared with 24-hour ambulatory cuff monitoring, especially at night.",
    "does_not_cover": "Watches with a built-in cuff, covered separately; hypertension notifications that report no number; diagnosis."
  },
  "limitations": [
    "Devices use different technologies, so pooled results may not apply to any one product.",
    "Several studies are small, and some authors have ties to device makers."
  ],
  "evidence": {
    "anchor": [
      {
        "key": "doi:10.1016/j.ajpc.2025.101342",
        "title": "Comparing the accuracy of continuous blood pressure monitoring using wearable cuffless devices with conventional 24-hour ambulatory blood pressure monitoring: A systematic review and meta-analysis",
        "first_author": "Insun Lee",
        "journal": "American Journal of Preventive Cardiology",
        "year": 2025,
        "url": "https://doi.org/10.1016/j.ajpc.2025.101342",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1038/s41598-023-33205-z",
        "title": "Method-comparison study between a watch-like sensor and a cuff-based device for 24-h ambulatory blood pressure monitoring.",
        "first_author": "Proença",
        "journal": "Scientific reports",
        "year": 2023,
        "url": "https://doi.org/10.1038/s41598-023-33205-z",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": [
            "conflict statement: the authors' institute holds the patent on the method tested, and two authors are its inventors"
          ]
        }
      }
    ],
    "conflicting": [
      {
        "key": "doi:10.1097/hjh.0000000000003960",
        "title": "Evaluation of Aktiia cuffless blood pressure monitor across 24-h, daytime, and night-time measurements versus ambulatory monitoring: a prospective, single-centre observational study.",
        "first_author": "Almeida",
        "journal": "Journal of hypertension",
        "year": 2025,
        "url": "https://doi.org/10.1097/HJH.0000000000003960",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [
            "Aktiia"
          ],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1097/hjh.0000000000003428",
        "title": "Evaluation of the ability of a commercially available cuffless wearable device to track blood pressure changes",
        "first_author": "Isabella Tan",
        "journal": "Journal of Hypertension",
        "year": 2023,
        "url": "https://doi.org/10.1097/hjh.0000000000003428",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": [
            "conflict statement: Aktiia supplied the devices tested, and two authors have been paid by Aktiia"
          ]
        }
      }
    ],
    "supporting": [
      {
        "key": "doi:10.1097/mbp.0000000000000804",
        "title": "Photoplethysmography based remote cardiac blood pressure monitoring compared with 24-h ambulatory blood pressure monitoring.",
        "first_author": "van Vliet",
        "journal": "Blood pressure monitoring",
        "year": 2026,
        "url": "https://doi.org/10.1097/MBP.0000000000000804",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1038/s41440-026-02759-6",
        "title": "Validation of ring-type cuffless blood pressure (BP) monitoring device for detecting awake-asleep BP variations compared to ambulatory BP monitoring device.",
        "first_author": "Lee",
        "journal": "Hypertension research : official journal of the Japanese Society of Hypertension",
        "year": 2026,
        "url": "https://doi.org/10.1038/s41440-026-02759-6",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": [
            "funding statement: sponsored by Sky Labs, maker of the CART BP ring tested, which took part in study design and data collection"
          ]
        }
      },
      {
        "key": "doi:10.3390/s23187931",
        "title": "Nocturnal Blood Pressure Estimation from Sleep Plethysmography Using Machine Learning.",
        "first_author": "Yilmaz",
        "journal": "Sensors (Basel, Switzerland)",
        "year": 2024,
        "url": "https://doi.org/10.3390/s23187931",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ]
  },
  "evidence_last_evaluated": "Oct 19, 2026",
  "rating_history": [
    {
      "date": "2026-10-19",
      "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-blood-pressure#cuffless_nighttime_accuracy",
  "related_findings": [
    "https://knowyourprime.com/evidence-calibrated-cuffless-blood-pressure-tracking",
    "https://knowyourprime.com/evidence-smartwatch-cuff-blood-pressure-accuracy"
  ],
  "related_articles": [
    "https://knowyourprime.com/can-a-smartwatch-measure-blood-pressure",
    "https://knowyourprime.com/does-cuffless-blood-pressure-wearable-actually-work"
  ],
  "methodology": "https://knowyourprime.com/methodology",
  "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0021, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-cuffless-blood-pressure-at-night"
}