Apple Watch health features: the smartwatch to beat on health metrics

When Apple put a working EKG on a wrist in 2018, it was the only direct-to-consumer device that could make that claim. Eight years and several watchOS updates later, the Apple Watch is still the smartwatch other brands measure themselves against on health metrics: ECG and irregular rhythm alerts, sleep apnea notifications validated against thousands of nights of clinical data, and hypertension pattern alerts most competitors don't offer at all.

None of that makes it a diagnostic device. Every feature below is a screening tool: a health companion quietly working in the background, built to flag something worth a doctor's attention, not to replace one.

ECG, irregular rhythm notifications, sleep apnea detection, and hypertension pattern alerts sit in a category of one: doctors already use this data to help guide real treatment decisions, like adjusting how often a patient needs a blood thinner instead of a fixed year-round prescription. That's a different league from a step counter.

Not every Apple Watch has every feature though: the model you pick decides what you get, covered in the comparison below.

Browse the full Apple Watch range available on refurbed to compare current models and pricing.

Picture your chest rising and falling as you breathe. That same oscillation shows up as tiny movements at your wrist, and the Apple Watch's accelerometer picks it up. Machine learning models trained on that signal flag interruptions of 20 to 30 seconds, the kind of shallow or paused breathing associated with sleep apnea.

Wear the watch for at least 10 nights within a rolling 30-day window, and the Health app shows a nightly ‘breathing disturbances’ reading: elevated or not elevated. Apple built the feature around that 30-day view instead of single-night alerts, to smooth out normal night-to-night swings from alcohol, sleep position, or a rough night's rest.

The validation behind it is substantial: over 11,000 nights of ground-truth sleep lab and at-home recordings, plus another 1,500 nights for the FDA submission. Apple is the second major smartwatch maker to ship sleep apnea detection, after Samsung's Galaxy Watch. The two approaches differ sharply: Samsung needs just 2 nights of data and folds in blood oxygen readings, while Apple relies on the accelerometer and machine learning alone over the full 30 days.

As with every feature here, no smartwatch can diagnose sleep apnea on its own. A consistently elevated reading is worth a conversation with a doctor, ideally backed by a proper sleep study.

Four photodiodes on the back of the watch take a blood oxygen reading in about 15 seconds, on demand or periodically through the day. A normal resting range sits around 95 to 99%, though people with COPD or emphysema often run lower than that as their baseline. Home oxygen is typically considered below 88%. The feature earned its ‘silent hypoxia’ nickname during the pandemic, when a dropping reading became an early warning sign before symptoms caught up.

Fall detection combines the accelerometer and gyroscope to recognize a hard fall, and calls emergency services automatically after about a minute of no movement. The CDC estimates over 800,000 older adults are hospitalized every year after a fall, exactly the population this feature was built for.

The Noise app tracks ambient sound against the World Health Organization's safe listening threshold of 80 decibels over 40 hours a week, and alerts you once you hit that weekly dose. Around 1 in 5 teenagers already has some hearing loss, roughly 30% higher than two decades ago.

Not every feature lands as pure convenience. Hand-washing detection, which listens for the sound of soap and running water, unsettles some people more than it reassures them. Fair enough. It's still one of the more literal examples of a watch quietly working in the background.

Not every Apple Watch gives you the same health suite. Series 11 carries the full ECG, blood oxygen, and hypertension package, the model to reach for if health tracking is the priority. Ultra 3 shares that same sensor generation in a larger, more rugged case. SE 3 trades ECG and blood oxygen for a lower price, but keeps sleep apnea notifications and fall detection.

Here's exactly what each model unlocks.

Cardiologist Rod Passman at Northwestern Medicine puts it plainly: a watch flagging something wrong isn't the same as a diagnosis. He's running NIH-funded research into watch-guided anticoagulation, using rhythm data to decide when a patient needs a blood thinner instead of a fixed year-round dose, balancing the benefit against the bleeding risk.

Sleep specialist Matt Bianchi makes the same point about sleep apnea notifications: no smartwatch can give a medical diagnosis on its own.

Doctors don't insist on the Apple Watch specifically either. Samsung, Fitbit, and Cardia all come up as legitimate options, chosen based on what phone a patient already owns and what they can afford. Worth keeping in mind before assuming Apple is the only real choice.

Series 11 still leads on raw health sensing, but it's worth seeing by how much. Galaxy Watch 8, Pixel Watch 4, and Huawei Watch GT 3 Pro all track heart rate, movement, and temperature reliably. None of them match the ECG, sleep apnea, or hypertension detection on the Apple side, and their spec sheets don't claim to.

If you have a cardiac history or you're buying for an older parent, Series 11 or Ultra 3 make the most sense: ECG, fall detection, and hypertension alerts all matter more at that stage of life. Ultra 3 is worth the extra size and weight only if you're also outdoors a lot and want the longer battery life that comes with it.

Don't need ECG and want to spend less? SE 3 still gives you sleep apnea notifications, fall detection, and continuous heart rate tracking.

On Android, or just after a lower entry price with solid everyday tracking, the Galaxy Watch 8 or Pixel Watch 4 cover heart rate, movement, and sleep tracking well. Just don't expect ECG or sleep apnea detection from either.

Refurbished also stretches your budget further: a refurbished Series 10 gets you the same ECG-capable sensor as the newest models, for less.

Is the Apple Watch ECG accurate?

Yes, within its intended use. Apple's clinical trial measured 99.6% specificity for sinus rhythm and 98.3% sensitivity for atrial fibrillation, and it's a single-lead reading, not a full 12-lead hospital EKG.

Can a smartwatch diagnose AFib or sleep apnea?

No. Every feature here is a screening tool. A flagged reading is a reason to see a doctor, not a diagnosis on its own.

Which Apple Watch has blood oxygen and hypertension notifications?

Series 11 and Ultra 3 ship with both, and the feature also reached Series 9, Series 10, and Ultra 2 through a software update, since they share the same sensor generation.

Do other smartwatches have ECG like the Apple Watch?

Rarely at this price point. The comparison above shows exactly where the gap sits today.