{ "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-0018", "version": "1.0", "reviewed": "2026-10-24", "url": "https://knowyourprime.com/evidence-smartwatch-blood-oxygen-at-altitude", "title": "Smartwatch Blood Oxygen Accuracy at Altitude", "question": "Can a smartwatch blood oxygen reading be trusted at altitude?", "measurement": "Blood oxygen (SpO2)", "devices": [ "Garmin", "Smartwatch" ], "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 at real altitude on the evidence so far. A Garmin watch read close to the reference at rest in simulated altitude below about 12,000 feet, but two field studies at 4,559 and 4,800 meters found Garmin watches reading too high, which is the dangerous direction for a climber deciding whether to keep going.", "reasoning": [ "At altitude, oxygen saturation falls and the reading matters most for safety. One laboratory study at rest affirms that a Garmin fenix tracks closely at most simulated altitudes, which is the clean anchor.", "Two studies at real altitude contradict it. One compared a Garmin with arterial blood at 4,559 meters and found large overestimation; the other found a Garmin’s readings untrustworthy up to 4,800 meters and concluded its use for judging acclimatization should be proscribed. With an affirming anchor and a core-hitting conflict, the rule rates the claim Uncertain." ], "key_results": [ { "text": "In normobaric hypoxia at rest, a Garmin fenix overestimated SpO2 by 0.7 to 0.8 percent at most simulated altitudes, except at 12,000 feet, where it did not hold.", "source": "doi:10.1080/02701367.2020.1759768", "source_url": "https://doi.org/10.1080/02701367.2020.1759768", "source_citation": "Lauterbach et al., Research Quarterly for Exercise and Sport, 2021" }, { "text": "At 4,559 meters in 13 healthy lowlanders, a Garmin Fenix 5X Plus read 7.0 points above arterial blood saturation on average (limits of agreement -6.5 to 20.5, MAPE 9.77 percent, ICC 0.549), while a medical monitor agreed well.", "source": "doi:10.3390/s21196363", "source_url": "https://doi.org/10.3390/s21196363", "source_citation": "Schiefer et al., Sensors, 2021" }, { "text": "A Garmin Forerunner 245 read SpO2 higher than the reference with an error rate above 50 percent overall and above 80 percent above 4,800 meters; the authors concluded its use for altitude acclimatization should be proscribed.", "source": "doi:10.1055/a-1337-2790", "source_url": "https://doi.org/10.1055/a-1337-2790", "source_citation": "Hermand et al., International Journal of Sports Medicine, 2021" } ], "scope": { "applies_to": "Wrist-worn consumer blood oxygen readings at simulated and real high altitude, compared with arterial blood or a medical oximeter.", "does_not_cover": "Brands other than Garmin, which have little or no altitude testing; altitude sickness diagnosis; aviation use." }, "limitations": [ "All three studies tested Garmin devices, with 10 to 13 participants in the field studies.", "Simulated altitude in a lab at rest is easier than real altitude with cold hands and movement." ], "evidence": { "anchor": [ { "key": "doi:10.1080/02701367.2020.1759768", "title": "Accuracy and Reliability of Commercial Wrist-Worn Pulse Oximeter During Normobaric Hypoxia Exposure Under Resting Conditions.", "first_author": "Lauterbach", "journal": "Research quarterly for exercise and sport", "year": 2021, "url": "https://doi.org/10.1080/02701367.2020.1759768", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } }, { "key": "doi:10.3390/s21196363", "title": "Validity of Peripheral Oxygen Saturation Measurements with the Garmin Fēnix® 5X Plus Wearable Device at 4559 m", "first_author": "Lisa Maria Schiefer", "journal": "Sensors", "year": 2021, "url": "https://doi.org/10.3390/s21196363", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } } ], "conflicting": [ { "key": "doi:10.1055/a-1337-2790", "title": "Accuracy and Reliability of Pulse O2 Saturation Measured by a Wrist-worn Oximeter.", "first_author": "Hermand", "journal": "International journal of sports medicine", "year": 2021, "url": "https://doi.org/10.1055/a-1337-2790", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } } ], "supporting": [ { "key": "doi:10.1177/15578682251398399", "title": "Association Between Decreased Pulse Oximetry and Acute Mountain Sickness Upon Rapid Ascent to 4,086 m Among Young Chinese Men.", "first_author": "Tang", "journal": "High altitude medicine & biology", "year": 2026, "url": "https://doi.org/10.1177/15578682251398399", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } }, { "key": "doi:10.1016/j.wem.2012.11.009", "title": "Measuring arterial oxygenation in a high altitude field environment: comparing portable pulse oximetry with blood gas analysis.", "first_author": "Ross", "journal": "Wilderness & environmental medicine", "year": 2013, "url": "https://doi.org/10.1016/j.wem.2012.11.009", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } }, { "key": "doi:10.1152/japplphysiol.00409.2001", "title": "Validity of pulse oximetry during maximal exercise in normoxia, hypoxia, and hyperoxia.", "first_author": "Yamaya", "journal": "Journal of applied physiology (Bethesda, Md. : 1985)", "year": 2002, "url": "https://doi.org/10.1152/japplphysiol.00409.2001", "industry_ties": { "checked": true, "author_affiliations": [], "funders": [], "stated_ties": [] } } ] }, "evidence_last_evaluated": "Oct 25, 2026", "rating_history": [ { "date": "2026-10-02", "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-spo2#altitude_accuracy", "related_findings": [ "https://knowyourprime.com/evidence-wearable-blood-oxygen-accuracy" ], "related_articles": [ "https://knowyourprime.com/wearable-spo2-accuracy-at-altitude" ], "methodology": "https://knowyourprime.com/methodology", "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0018, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-smartwatch-blood-oxygen-at-altitude" }