Inside the Apple Watch Series 10's New Sleep Apnea Detection Feature

Learning whether you have a sleep disorder like sleep apnea typically requires what many would likely consider to be an uncomfortable night's rest, with sensors placed all over your body and even inside your nose.

The Apple Watch can't replicate a sleep study or diagnose sleep conditions, and it's not trying to. But Apple wants to help people figure out whether they should at least speak with their doctor about getting one. 

The new Apple Watch Series 10, along with the Series 9 and Ultra 2, is able to detect signs of moderate to severe sleep apnea, a sleep disorder in which breathing stops and starts overnight and is estimated to affect 936 million adults around the world. The new watch feature, which works by measuring movements in the wrist associated with breathing interruptions, was cleared by the Food and Drug Administration on Monday. It will ship on the Series 10 at launch and is available for other compatible watches with the release of WatchOS 11.

Watch this: How Apple's Sleep Apnea Feature Works on Apple Watch

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Of the roughly 30 million people in the US with sleep apnea, which is linked to an increased risk of type 2 diabetes and other health complications if left untreated, only 6 million have been diagnosed, according to a 2022 article from the American Medical Association. That indicates many people may not know they have the disease, which is where tools like Apple's new sleep apnea notification could potentially help. 

And according to Dr. Matt Bianchi, a research scientist on Apple's Health Technologies team, it took more than 11,000 nights of sleep recordings to get it right. 

"One of the ways we make sure that we don't make mistakes or misconstrue movements like that is to collect an incredible amount of ground truth data across a huge variety of people, sleeping in the lab, in a sleep center, sleeping at home in their natural environment," Bianchi said in a virtual interview with CNET about how Apple developed the feature.

Smartwatches are all about health tracking

Back in 2019, Apple CEO Tim Cook told CNBC that the company's "greatest contribution to mankind" would be "about health," and the Apple Watch has clearly played an important role in making progress toward that goal. 

The Apple Watch started as a niche luxury iPhone accessory nearly a decade ago, but over the last 10 years it has evolved into a comprehensive health monitoring device capable of detecting irregular heart rhythms, whether you've taken a hard fall and changes in body temperature among a slew of other health and wellness data points. Sleep apnea detection is yet another step in that direction. 

"Even after a short period of time, we started to hear from users who were noticing things about their health and fitness that they maybe would not have noticed before," Deidre Caldbeck, senior director for Apple Watch and Health product marketing at Apple, said regarding the Apple Watch's health tracking features. "So we started to pull on those threads."

Apple's not alone; the announcement comes at a time when rivals like Samsung and Google are also pushing their own wearable devices forward with new health tracking capabilities. Samsung announced that its latest Galaxy Watches would be able to measure signs of sleep apnea in July, while Google's Pixel Watch 3 can detect a loss of pulse. Taken together, these updates are another sign that smartwatches are continuing to grow into much more than just activity and exercise trackers. 

"Smartwatches have always been about health and fitness, make no mistake," Ramon Llamas, research director for the International Data Corporation, said over email. "It's a question of how much deeper we can go."

How the Apple Watch detects sleep apnea

Sleep apnea is usually diagnosed through a sleep study or an at-home sleep apnea test. A sleep study, or polysomnogram, involves wearing sensors for measuring brain waves that occur during stages of sleep, an ECG sensor for monitoring heart activity, sensors for detecting muscle and eye movement, breathing sensors for monitoring airflow and a pulse oximeter for blood oxygen readings, according to the Cleveland Clinic. (My colleague Lexy Savvides experienced this firsthand when exploring how to use tech to improve the quality of her sleep earlier this year).

The main benefits of devices like the Apple Watch that can pick up on signs of sleep apnea at home is that doctors have more nights worth of data to work with. Plus, it could help encourage people to speak with their doctor before the condition worsens.

"We should welcome [smartwatches] as tools," Dr. Rafael Pelayo, a sleep specialist and clinical professor at Stanford Medicine, told CNET's Lexy Savvides."If you get a sleep test, you're going to get one night, maybe two nights."

The Apple Watch is brimming with sensors, including the ability to take an ECG. Versions of the Apple Watch sold outside the US can also measure blood oxygen, but that feature is no longer available on units sold in America because of a patent dispute with health tech company Masimo.

Still, there's one Apple Watch sensor that plays a primary role in picking up potential sleep apnea signals: the motion-detecting accelerometer. Your chest oscillates as you breathe overnight, and these subtle movements are reflected in your arm so they can be detected on the wrist using the watch's accelerometer, Bianchi says. These readings manifest in a new metric called breathing disturbances, which are logged in the Apple Health app. The feature works the same regardless of whether you have an Apple Watch with the blood oxygen feature.

"When you have an interruption in breathing where you're either taking more shallow breaths, or you stop breathing for 20 or 30 seconds, that can be read out and detected through machine learning algorithms," Bianchi said.

The chips inside the Apple Watch Series 10, Series 9 and Ultra 2 are also a large part of what drives the Apple Watch's sleep apnea detection, Caldbeck said, which is why the feature is available only on those models. An algorithm analyzes breathing disturbance data on the watch and will send a notification if signs of sleep apnea are present.

"It's the ability to use the accelerometer data, process that data on device, and ensure that we get accuracy, and ensure we meet our performance objectives," Caldbeck said. "And so we really needed that combination."

But sleep apnea isn't the only reason why you may experience a breathing disturbance overnight; factors like alcohol consumption, congestion from illness and your position while sleeping can also have an impact. That's why the Apple Watch looks for breathing disturbances over a 30-day window before sending that notification. 

However, you need only to wear the watch for at least 10 nights within that window for the feature to work. That 10-night minimum strikes the right balance of being realistic (not everyone wears their watch to bed religiously every night), while still collecting enough data.

"We don't want to react to the incidental three days of a long weekend or brief illness," Bianchi said. "We want to make sure that we're capturing what is really you."

11,000 nights of sleep data

As part of the clinical validation process, Apple worked with academic medical centers' hospital systems and clinical research organizations to gather the more than 11,000 nights of sleep data. 

On top of that, it collected an additional 1,500 nights worth of sleep data as part of the FDA regulatory process, which Bianchi says is the largest validation study submitted to the FDA for clearance of a sleep apnea technology. Aside from these steps that were taken as part of the clinical validation process, Apple also has its own internal sleep lab for prototyping and developing its sleep tracking features.

Among the biggest challenges was making sure Apple had a large and diverse enough data set to account for every way in which the technology could make a mistake. 

"Any clinical level validation, anything that meets that bar for regulatory, the confidence we need to have to say we're behind this feature is next level," Bianchi said.  

Those with a compatible Apple Watch will be able to view nightly breathing disturbances in the iPhone's Health app regardless of whether they receive an alert. Since some breathing disturbances are considered typical, Apple labels breathing disturbances as "elevated" or "not elevated," with an elevated number of disturbances over multiple nights potentially signaling sleep apnea. The notification also encourages users to have a conversation with their doctor and provides an easy way to export the relevant data. 

The way Apple communicates and provides context around these readings is particularly important now that the Apple Watch and other wearables are sophisticated enough to spot potential health issues. A paper published in the Cardiovascular Digital Health Journal in August 2020 suggests smartwatches can contribute to health-related anxiety, citing an example of a 70-year-old woman who believed smartwatch notifications were a sign of "worsening cardiac function." She took 916 ECGs over the course of a year.

Smartwatch maker Withings is also attempting to address this concern by providing clinical reviews of heart health data from certified cardiologists as part of its recently announced Cardio Check-Up feature. 

But when it comes to sleep apnea, clinicians like Pelayo hope it'll be possible to detect it even sooner down the line. 

"I really want something to pick up the mild sleep apnea," he said. "That's hopefully where the future will lie for us."