IT Home, October 13: At 1:00 AM on October 14, Apple pushed a new system update to users via OTA. After upgrading to iOS and watchOS, Apple Watch users will be able to enable the sleep apnea feature. This function has previously been approved by the National Medical Products Administration as a Class II medical device under the name “Sleep Apnea Alert,” becoming another regulated health feature on the Apple Watch.
The sleep apnea feature is currently available on Apple Watch Series 9, Ultra 2, and SE 3, as well as later models, for adult users aged 18 and older who have not previously been diagnosed with sleep apnea.
This year marks the eleventh anniversary of the Apple Watch’s release, and its health features now span 18 areas. Sleep has consistently been a core focus, with Apple gradually transforming the watch into a personal sleep observer through features like bedtime reminders, sleep stages, sleep scores, and vital sign monitoring. The addition of sleep apnea detection shifts user attention from “how well you sleep” to “how healthy your sleep is.”
Eighty percent of patients are unaware they are sick.
“One of the most widespread misconceptions is that snoring means you’re sleeping well.” After falling asleep, soft tissues in the throat and the relaxed, falling-back tongue may obstruct the upper airway. A complete cessation of airflow for more than 10 seconds is classified as an apnea event; if the airway is not fully blocked but airflow is significantly reduced accompanied by a drop in blood oxygen levels, it is called hypopnea. The full name of this condition is Sleep Apnea-Hypopnea Syndrome, with obstructive sleep apnea being the most common form. Diagnosis is made when the Apnea-Hypopnea Index (AHI) reaches or exceeds five events per hour on average.
Its prevalence exceeds what most people imagine. A 2019 study in The Lancet Respiratory Medicine showed that the global prevalence has risen from 2% to 4% over a decade ago to more than 24%, with over 1 billion patients aged 30 to 69 alone; China has approximately 176 million patients, the highest number worldwide.
More challenging is the diagnostic gap, as approximately 80% of patients are unaware they have the condition. While being overweight and having a short, thick neck are significant risk factors, structural issues such as a small jaw, deviated septum, enlarged tonsils, and an enlarged tongue also place many thin individuals at risk—some patients may even present with symptoms like insomnia or anxiety.
Each episode of apnea is accompanied by hypoxia and carbon dioxide retention; repeated micro-arousals fragment sleep, and the intense negative pressure fluctuations in the chest continuously strain the heart and blood vessels. According to clinical data obtained from Apple, approximately 80% of treatment-resistant hypertension is associated with sleep apnea, the risk of coronary heart disease increases fivefold, 60% to 90% of stroke patients have this condition, and 46% of all sudden cardiac deaths occur at night; the risk of car accidents also rises to seven times that of the general population.
See your breath through subtle movements of your wrist.
The Apple Watch takes a different approach from traditional blood oxygen monitoring. According to Apple, the new chip introduced with Series 9, combined with the accelerometer, has a range of up to 256g, enabling it to detect extremely subtle, imperceptible muscle movements in the wrist during overnight wear. When breathing becomes disrupted, these muscles exhibit tiny vibrations synchronized with respiration. The watch identifies each such anomaly and converts them into a new metric—the Respiratory Disturbance Index—measured in "events per hour"—to reflect the degree to which normal breathing is interrupted.
Apple's explanation is that they evaluated various data sources and determined that the accelerometer alone is sufficient to achieve the design goals, while blood oxygen monitoring is conducted intermittently and may not align with every breathing event.
At the operational level, functionality is evaluated over a 30-day cycle. Users must wear the device for at least 10 nights within that period—consecutive nights are not required. The system reviews the data from this timeframe; if more than half of the nights show an increase in the respiratory disturbance index, the Apple Watch will send a notification indicating potential signs of moderate to severe sleep apnea. If fewer than 10 nights of data are available, no notification is triggered.
Apple stated that sleep apnea is a chronic condition rather than an acute emergency; a 30-day observation period meets screening requirements and ensures more rigorous assessment. Factors such as alcohol consumption, upper respiratory infections, certain medications, exercise, and weight changes can all elevate respiratory disturbance levels, and these fluctuations can be identified in the health trends within the Health app.
Apple also revealed that over 11,000 nights of paired data were used to train the algorithm, with participants wearing an Apple Watch while undergoing clinical-grade sleep monitoring. Reference devices included hospital-based polysomnography (PSG) and home sleep apnea tests (HSAT), and events were determined using a strict criterion of a 4% drop in blood oxygen to minimize false positives.
During the clinical validation phase, nearly 1,500 participants wore the watch for up to 30 consecutive nights and completed two nights of HSAT testing as a control. The results showed a sensitivity of 66.3% and a specificity of 98.5% for this feature; no participants without sleep apnea received a false positive, and sensitivity reached 89.1% among severe cases.
There are eligibility requirements—please take the notification seriously.
Access to this feature has clear eligibility requirements: users must be at least 18 years old and have never been diagnosed with sleep apnea; those already diagnosed do not need to enable it. Its true target is individuals who are unsure whether they have the condition or suspect they might, but have never sought medical evaluation. Apple repeatedly emphasizes that this feature provides only a risk alert and cannot be used for diagnosis, treatment, or management, nor does it replace traditional medical care; even if no issues arise after 30 days, it does not guarantee complete peace of mind.
If the notification does arrive, Apple recommends taking it seriously, consulting a doctor as soon as possible, and exporting your breathing disturbance data as a PDF report to bring to your appointment. This approach has precedent.
An Apple employee enabled this feature while on a business trip in the U.S. After wearing it for 30 days, he received a notification and was later diagnosed with severe sleep apnea caused by nasal structural issues that obstructed breathing when lying on one side. After using a CPAP machine, his sleep data stabilized, and for the first time, he experienced the feeling of waking up refreshed and alert. His doctor said it’s rare to see patients who catch such conditions this early, rather than waiting until heart problems arise.
Regarding privacy, Apple states that health data is fully encrypted and stored on the device, and even when synced to iCloud, it is done so in an encrypted manner.
Conclusion
For a long time, diagnosing sleep apnea relied on polysomnography in hospitals, which requires round-the-clock supervision by medical professionals and occupies a hospital bed. With hundreds of millions of potential patients, such resources are woefully inadequate. The Apple Watch brings the initial screening to the wrist, using observations over multiple consecutive nights to address the limitation of traditional tests, which typically cover only one or a few nights.
The watch provides only a hint and should not be treated as a diagnosis. It acts more like a ticket, guiding individuals unaware of sleep apnea toward proper evaluation and treatment. If you're an Apple Watch user who has updated your system, take a moment to review your respiratory irregularity data—you'll likely feel even more at ease.