Watch pulse oximeters offer convenient, continuous monitoring but vary in accuracy, with some studies showing devices like Apple Watch closer to clinical standards than others (e.g., Garmin), though all can be affected by skin tone and movement; they're great for trends but not medical-grade diagnosis, needing validation with clinical devices for critical health decisions.
The overall accuracy was 84.9% for the Apple Watch and 78.5% for the Withings ScanWatch. The Spearman rank correlation coefficients reported a moderate correlation to ward-based photoplethysmography (Apple: rs=0.61; Withings: rs=0.51, both P<. 01).
A moderate correlation was found between smart watch and blood gas SpO2 measurements (ICC: 0.502, p: 0.004). Bland-Altman analysis revealed a mean error of −1.79% between the watch and blood gas, with limits of agreement ranging from −7.43% to 4.87% (SD: 5.54).
It's very difficult to know if your pulse oximeter is inaccurate without comparing it with a reading from a medical-grade device or a blood sample. But it's important to remember that pulse oximeter readings are only an estimate of your blood oxygen levels.
The mean spO2 measured with the conventional pulse oximeters was 94.4%. The mean spO2 measured with the Apple Watch was 95.9%. The Pearson correlation coefficient between watch and conventional oximeter measurements was 0.81, with limits of agreement of -2.7% and +4.1%.
People should contact a health care provider if their oxygen saturation readings drop below 92%, as it may be a sign of hypoxia, a condition in which not enough oxygen reaches the body's tissues.
Cardiologists view the Apple Watch as a useful wellness tool for general heart awareness and detecting potential issues like atrial fibrillation (AFib), but not as a replacement for clinical devices, stressing it can't diagnose heart attacks or provide full diagnostic ECGs. They appreciate its ability to prompt users to seek care for irregularities, but caution against over-reliance due to risks of false positives, movement interference, and its single-lead limitation compared to 12-lead ECGs, emphasizing that symptoms always require a doctor's evaluation.
Vital Signs
It may be helpful to have a baseline as some patients living with lung disease can tolerate low oxygen levels for months and months. Generally, if the oxygen level is 79% or lower, they will likely die in the next 24 hours.
Which finger to use in a pulse oximeter? As per the studies, your right hand's middle finger shows the best results. Make sure to take off any nail polish and avoid using on cold fingers as the readings may not show correctly.
“Be aware that multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish.”
Cardiologists often recommend smartwatches like the Apple Watch (Series 9/10), Samsung Galaxy Watch (5/6+), Fitbit Sense 2, and Withings ScanWatch for their advanced heart-sensing features like ECG, AFib detection, and continuous heart rate monitoring, which help track heart rhythms and share data with doctors, though they aren't diagnostic replacements for medical tests. The best choice depends on your phone (Apple for iPhone, Samsung for Android) and specific needs (fitness vs. medical insights).
Oxygen saturation (SpO2) is a measurement of how much oxygen your blood is carrying as a percentage of the maximum it could carry. For a healthy individual, the normal SpO2 should be between 96% to 99%. High altitudes and other factors may affect what is considered normal for a given individual.
The blood oxygen (SpO₂) feature can sometimes flag issues (like very low oxygen at high altitudes or in some COVID cases), but it's generally not as precise as a medical-grade fingertip pulse oximeter.
Using SpO2 sensors, smartwatches emit light through your wrist and measure reflected light with photodiodes. Algorithms then estimate oxygen saturation by analyzing light absorption.
In 2021, Masimo sued Apple, claiming the Apple Watch maker infringed on one of its patents for optical blood monitoring. A judge ruled that Apple infringed on the patent, and the International Trade Commission upheld that ruling. Apple was forced to suspend sales of the two offending products from 2023 to 2024.
A typically healthy range is 95% to 100%, but factors like exercise, elevation and health conditions can affect your results. For best results, rest at least 5 minutes before measuring, stay still and comfortable during measurement. Individual results may vary.
Contact your provider if your oxygen saturation level is 92% or lower. If it falls to 88% or lower, seek immediate medical attention. If you have questions about your results, talk to your provider.
Shortness of breath does not always indicate that you are hypoxic. In other words, your level of dyspnea, or air hunger, does not always correlate with your oxygen saturation. This means that you can be short of breath, even extremely short of breath, even in the presence of normal oxygen saturation.
As you rest, your lungs and blood work together to keep oxygen flowing to your brain and vital organs. While it's normal for oxygen levels to dip slightly during sleep, especially in deeper stages, significant drops can signal an underlying issue.
Final stage (minutes before death).
In the last minutes of life, breathing becomes shallow and may stop altogether. The heartbeat slows and eventually ceases. The body may make reflexive movements, such as small twitches, but these are not signs of pain or distress.
Silent hypoxia (also known as happy hypoxia) is generalised hypoxia that does not coincide with shortness of breath. This presentation is known to be a complication of COVID-19, and is also known in walking pneumonia, altitude sickness, and rebreather diving.
Yes, a weak heart can often become stronger or significantly improve with consistent effort, involving a doctor-guided plan with regular exercise, a heart-healthy diet (low sodium), medications, stress management, quitting smoking, limiting alcohol, and managing other conditions like high blood pressure or diabetes to improve heart function and quality of life.
An ECG can diagnose a current or previous heart attack. The patterns on the ECG results can help a healthcare professional learn which part of the heart is damaged. Blood and oxygen supply to the heart.
Apple Watch cannot detect heart attacks. If you ever experience chest pain, pressure, tightness, or what you think is a heart attack, call emergency services immediately. The irregular rhythm notification feature on Apple Watch is not constantly looking for AFib.