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Samsung Health’s blood oxygen readings are best treated as wellness estimates, not exact clinical measurements. A published study found reasonable agreement for the Galaxy Watch 4 during sleep, but it does not establish accuracy for every Galaxy Watch, daytime spot checks, or any individual reading. The U.S. Food and Drug Administration (FDA) advises people not to rely on a pulse oximeter reading alone.
What does the accuracy evidence show?
A 2022 study in Sleep Health evaluated oxygen saturation measured by the Galaxy Watch 4, which uses wrist-based reflectance pulse oximetry. The study enrolled 97 adults with sleep disturbances and compared simultaneous watch readings with a transmittance pulse oximeter used during polysomnography. That supports a narrow conclusion about this model in a sleep-study setting—not a general accuracy claim about all Samsung watches or Samsung Health readings.
The study authors reported an overall root mean squared error (RMSE) of 2.3% and a bias of −0.2%. RMSE summarizes the size of errors across the study data; it does not mean each reading was within 2.3 percentage points of the reference. Bias describes average direction of error, not the reliability of an individual result. Read the Galaxy Watch 4 study in Sleep Health.
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Results by sleep apnea severity
The study reported different RMSE values across obstructive sleep apnea severity groups:
| Study group | RMSE reported by the study authors |
|---|---|
| Normal | 1.65 ± 0.57% |
| Mild obstructive sleep apnea | 1.76 ± 0.65% |
| Moderate obstructive sleep apnea | 1.93 ± 0.54% |
| Severe obstructive sleep apnea | 2.93 ± 1.71% |
These are results for the 2022 study population and its sleep-measurement setup; they are not predicted error ranges for a particular watch owner.
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Does the study show that a Galaxy Watch can diagnose sleep apnea?
No. In the study, a Galaxy Watch 4 oxygen desaturation index threshold of at least 5 per hour was assessed as a predictor of a polysomnography apnea-hypopnea index of at least 15 per hour. The authors reported sensitivity of 89.7%, specificity of 64.1%, accuracy of 79.4%, and an area under the curve of 0.908. These are study-level results for that threshold and comparison, not evidence that a watch diagnoses sleep apnea or replaces a sleep study.
What can affect a wrist reading?
Samsung’s Galaxy Watch 3 instructions recommend wearing the watch snugly, covering its sensor, staying still, and not talking during measurement. Samsung’s developer guide also advises checking wrist position and pose and avoiding movement. These steps can improve measurement conditions, but they cannot guarantee accuracy. Samsung’s Galaxy Watch 3 measurement guidance and Samsung’s developer Measurement Guide explain the setup.
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The FDA lists poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and fingernail polish as factors that can affect pulse oximeter accuracy. These are general cautions about pulse oximetry; the Galaxy Watch 4 study did not quantify the effect of each factor for Samsung watches. See the FDA’s consumer guidance on pulse oximeters.
How should you use Samsung Health’s SpO₂ reading?
- Consider readings as wellness context or trends, not as a diagnosis or a precise substitute for clinical measurement.
- For a measurement, follow the instructions for your specific watch: keep the sensor in contact with the wrist, use the recommended position, and remain still.
- If a result seems concerning, consider how you feel as well as the number. Contact a healthcare professional for guidance, and seek care for serious or worsening symptoms.
- A fingertip pulse oximeter can provide another estimate, but it is also subject to pulse oximetry limitations and is not definitive on its own.
Samsung describes the Galaxy Watch 3 feature as wellness tracking and says that watch is not a medical device. The FDA likewise distinguishes general wellness products from medical-purpose devices; it says general wellness pulse oximeters are not evaluated for clinical decision-making or deciding whether to seek medical intervention. The FDA’s consumer instruction is direct: “Do not rely only on a pulse oximeter.”
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What the available evidence does not establish
- Accuracy across every Galaxy Watch generation or current Samsung model.
- Accuracy of daytime spot measurements; the cited study evaluated sleep measurements.
- Samsung-watch performance by skin pigmentation subgroup. The FDA identifies pigmentation as a potential general factor, but the study did not establish a Samsung-specific effect.
- A guarantee that an individual reading is close to a clinical reference, or that a watch reading can rule out a health problem.
In January 2025, the FDA issued draft guidance proposing recommendations for evaluating medical-purpose pulse oximeters, including consideration of skin pigmentation. It is explicitly nonbinding draft guidance, not a final rule or Samsung-specific approval. Read the FDA draft guidance.
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