What health metrics can the Apple Watch actually measure in 2026 — the complete sensor breakdown

TL;DR

Apple Watch is a wrist-worn sensor pack. As of May 2026 Apple sells three models — Apple Watch Series 11, Apple Watch Ultra 3 and Apple Watch SE 3 — and between them they carry an optical heart sensor (for heart rate, heart rate variability and the new hypertension pattern analysis), an electrical heart sensor (for the on-demand ECG), a Blood Oxygen sensor (for SpO₂), two wrist temperature sensors, an accelerometer and gyroscope (for motion, falls, crashes and sleep apnea pattern detection), a GPS receiver, an altimeter, a compass, a microphone for noise exposure, and — on Ultra 3 only — a depth gauge and water temperature sensor. The data lands in the iPhone Health app via Apple's HealthKit framework. None of these sensors are medical devices in the diagnostic sense; Apple's own product copy frames the readings as wellness signals and Apple's support pages explicitly tell you not to treat the notifications as a diagnosis.

The three Apple Watch models on sale in 2026

As of May 2026 Apple's current Apple Watch lineup is three models, all launched on 19 September 2025:

Apple Watch Series 11 is the mainstream model. It carries the full health sensor stack — optical heart sensor, electrical heart sensor for ECG, Blood Oxygen sensor, wrist temperature sensors, accelerometer, gyroscope, GPS, altimeter, compass, ambient light sensor, and microphone — and adds the hypertension notifications feature on the same hardware.

Apple Watch Ultra 3 is the larger, titanium-cased adventure model. It carries every sensor Series 11 carries, and additionally has a depth gauge and a water temperature sensor (suitable for recreational scuba diving to 40 metres with the Oceanic+ app), the most accurate GPS Apple has shipped in an Apple Watch, two-way satellite communications, and a 42-hour battery.

Apple Watch SE 3 is the value model. It has the optical heart sensor, the wrist temperature sensors (new to the SE line in this generation), the accelerometer and gyroscope, GPS, altimeter, compass and microphone. It does not have the electrical heart sensor (so there is no ECG app), it does not have the Blood Oxygen sensor, and per Apple Support the hypertension notifications feature is not available on Apple Watch SE.

Everything that follows describes the sensor stack at the device level. Where a sensor or feature is exclusive to a particular model, that is called out in the relevant section and again in the sensor-to-model matrix near the end.

The optical heart sensor

The optical heart sensor on the back of every current Apple Watch is a photoplethysmography (PPG) sensor: green and infrared LEDs shine light into the skin, photodiodes measure how much light comes back, and the variation in reflected light maps to the volume change in the blood vessels with each heartbeat. From that single underlying signal Apple derives most of the watch's heart-related metrics.

What the optical heart sensor produces, as exposed in the Health app:

• Heart rate (beats per minute). Sampled throughout the day, more densely during workouts and when motion is detected, and continuously during a recorded workout.
• Resting heart rate. A daily value computed from periods of stillness.
• Walking heart rate average. An average computed from steady walking sessions.
• Heart rate recovery. The drop in heart rate in the minutes after a workout ends.
• Heart rate variability (HRV). Apple Watch reports HRV as SDNN — the standard deviation of normal-to-normal beat intervals — sampled opportunistically throughout the day, plus a value taken during a Mindfulness breathing session. Apple does not expose RMSSD or pNN50 directly through HealthKit; consumer apps that report those values derive them from raw beat-to-beat intervals captured during workouts or from periodic measurements.
• High and low heart rate notifications. Apple Watch can alert you when your heart rate rises above or drops below thresholds you set in the Health app during periods of inactivity.
• Irregular rhythm notifications. A passive background check that can notify you if it detects a pattern suggestive of atrial fibrillation.
• Hypertension notifications. Launched in September 2025 on Apple Watch Series 9 and later and Apple Watch Ultra 2 and later, this feature analyses how a user's blood vessels respond to the beats of the heart over a rolling 30-day window and notifies you if it detects consistent signs of chronic high blood pressure. Per Apple's support page, the feature is only available to users 22 or older, is not for use during pregnancy, and is not for users already diagnosed with hypertension.

What the optical heart sensor does not produce: a systolic/diastolic blood pressure reading, a clinical-grade ECG trace, or a diagnosis of any condition. Apple's hypertension notification support page is explicit: "The Hypertension Notifications Feature is not intended to diagnose, treat, or aid in the management of hypertension."

The electrical heart sensor (ECG)

Series 11 and Ultra 3 — but not SE 3 — carry an electrical heart sensor integrated into the Digital Crown and the back crystal. When you place a finger on the Digital Crown, the watch completes a circuit across your body and records a single-lead electrocardiogram. Per Apple Support, the recording takes 30 seconds.

The ECG app produces a waveform and one of three classifications: Sinus Rhythm, AFib, or Inconclusive. ECG version 1 can classify AFib between 50 and 120 BPM; ECG version 2 can classify AFib between 50 and 150 BPM. The waveform and classification can be exported as a PDF and shared with a clinician.

Two things to be aware of for the ECG app:

• Country availability is not universal. Apple's per-feature watchOS feature availability page lists which regions have the ECG app cleared by the local regulator. Some countries class ECG tooling as restricted medical equipment, which is why Apple gates ECG by region of purchase as well as region of use. The version of the ECG app you get (v1 or v2) also depends on regulatory approval in your region.
• It is single-lead, not 12-lead. A clinical ECG is a 12-lead recording from electrodes placed across the chest. The Apple Watch records a single-lead recording from your wrist and a finger. It is useful for capturing intermittent arrhythmias that wouldn't show up in a brief office visit, and clinicians do use the exported PDF — but it doesn't substitute for a clinical ECG when one is indicated.

The Blood Oxygen sensor

A separate red and infrared LED cluster on the back of Apple Watch Series 11 and Apple Watch Ultra 3 measures peripheral blood oxygen saturation (SpO₂). The SE 3 does not have this sensor.

Two important details:

• The US data path is different. After an ITC import restriction tied to a patent dispute with Masimo, Apple introduced a redesigned Blood Oxygen feature for US users in August 2025: the sensor data from the watch is transmitted to the paired iPhone, the SpO₂ value is calculated on the iPhone, and the result appears in the Respiratory section of the Health app rather than on the watch face. Apple Watch Series 11 and Ultra 3 sold in the United States — specifically, units with part numbers ending in LW/A — use this same iPhone-calculated approach. Outside the United States, the calculation happens on the watch itself.
• Apple labels Blood Oxygen as wellness-only. Per Apple's Blood Oxygen support page, "Measurements taken with the Blood Oxygen app are not intended for medical use and are only designed for general fitness and wellness purposes." An Apple Watch SpO₂ reading is not interchangeable with the reading from a clinical pulse oximeter intended for medical monitoring.

The on-watch reading takes 15 seconds when initiated on demand. Apple Watch also takes background SpO₂ samples — most commonly during sleep when Track Sleep with Apple Watch is on. Apple notes that skin perfusion, motion, certain tattoos, and a resting heart rate above 150 BPM can prevent a successful reading.

Wrist temperature sensors

Apple Watch Series 11, Ultra 3 and — newly for this generation — SE 3 each carry two temperature sensors: one closer to the wrist and one inside the watch case. Apple uses the differential between the two, plus an algorithm that compensates for ambient temperature, to estimate wrist skin temperature during sleep.

Per Apple Support, wrist temperature data becomes available after about five nights of wearing the watch to bed with Sleep Tracking on. What you actually see in the Health app is not an absolute body-temperature value — it's a nightly deviation from your personal baseline, established over those first five nights. If you switch to a new Apple Watch, the baseline re-establishes over another five nights.

The Cycle Tracking app uses the same wrist temperature signal to produce retrospective ovulation estimates — that is, an estimate of the likely day ovulation already occurred, used to improve period prediction.

A few caveats Apple itself surfaces:

• It is wrist temperature, not core body temperature. The two correlate during sleep but not exactly.
• The retrospective ovulation estimate is, by name, retrospective. It is not a predicted ovulation date.
• Apple frames this signal as wellness and family-planning context, not as a contraceptive method or a fertility diagnostic.

The motion sensors: accelerometer and gyroscope

Every current Apple Watch carries a high-dynamic-range accelerometer and a gyroscope. These two sensors do a remarkable amount of work in the device.

Direct motion outputs:

• Step count, distance, flights climbed, activity calories, exercise minutes, stand hours — the underlying inputs to the Activity rings.
• Workout metrics: cadence, stride length, ground contact time, vertical oscillation, swim stroke and lap detection, SWOLF score, and — when combined with the optical heart sensor — heart rate zones, training load, cardio fitness (an estimated VO₂max), and cardio recovery.

Derived features that depend on the motion sensors:

• Fall Detection. The accelerometer and gyroscope together identify the signature of a hard fall, and after a brief countdown can place an Emergency SOS call.
• Crash Detection. A combination of accelerometer, gyroscope, microphone, barometer and GPS recognises the signature of a severe vehicle crash.
• Sleep tracking and sleep stages. While you sleep, the accelerometer detects micro-movement and the optical heart sensor measures heart rate variation; together they produce nightly estimates of sleep duration and time spent in REM, Core (light) and Deep sleep.
• Sleep apnea notifications. Per Apple Support, the watch uses the accelerometer to look for breathing disturbances at the wrist during sleep, categorises each night as Elevated or Not Elevated, and over a 30-day window notifies you if you consistently show patterns associated with moderate-to-severe sleep apnea. The feature requires Series 9 or later, Ultra 2, or SE 3, plus at least 10 nights of wear in the 30-day window, and the user must be 18 or older and not previously diagnosed with sleep apnea.
• Track running detection, double-tap and wrist-flick gestures, and the Action button on Ultra 3. All accelerometer-driven.

Location, elevation and depth

Three sensors handle the where-you-are stack:

• GPS. All three current models include GPS. Apple states that Apple Watch Ultra 3 has the most accurate GPS in any Apple Watch, with comparison testing in August 2025 against industry-leading dual-frequency sports watches. GPS is used for pace, distance and route tracking in outdoor workouts, and as one input to Crash Detection and to the satellite-emergency features on Ultra 3.
• Always-on altimeter. Reports elevation in real time and feeds Flights Climbed, plus elevation profiles for workouts. Standard on all three models.
• Compass. A magnetometer-based compass with Backtrack (the ability to retrace a path) and Waypoints, exposed in the Compass app.

On Apple Watch Ultra 3 only: a depth gauge and a water temperature sensor, both rated for recreational scuba diving with the Oceanic+ app down to 40 metres. Apple Watch Ultra 3 holds a 100-metre water-resistance rating to ISO 22810:2010. (Apple Watch Series 11 supports snorkelling to 6 metres.)

The microphone — noise exposure and hearing health

Each current Apple Watch carries a microphone array that is best known for calls and Siri, but it also runs a continuous-listening noise exposure classifier. The watch periodically samples ambient sound level (without recording or storing the audio), reports it in decibels, and can notify you when the surrounding noise level reaches a threshold known to put hearing at risk over time. The noise data lands in the Hearing section of the Health app.

The microphone is also one of several inputs into Crash Detection (the sound signature of a severe vehicle crash is part of the classifier), and powers the Walkie-Talkie and Voice Memos apps. It is not a clinical audiometer and Apple does not claim it is one.

What lands in the Health app

The sensors above don't store their data on the watch indefinitely. Readings are passed to the HealthKit framework on the paired iPhone, which makes them visible in the Health app and available to third-party apps you authorise. The categories of data the Apple Watch contributes include:

• Heart (heart rate, resting heart rate, walking heart rate average, HRV, heart rate recovery, irregular rhythm notifications, ECG recordings, high/low heart rate notifications, hypertension notifications)
• Respiratory (Blood Oxygen, respiratory rate, sleep apnea notifications)
• Body Measurements (wrist temperature)
• Activity (Move/Exercise/Stand, step count, distance, flights climbed, workouts and their per-workout metrics, cardio fitness)
• Sleep (in-bed time, asleep duration, sleep stages, sleep score)
• Cycle Tracking (cycle history, period prediction, retrospective ovulation estimate)
• Hearing (environmental sound levels, headphone audio levels, noise notifications)
• Mindfulness (mindful minutes, breathing sessions)

The Vitals app surfaces overnight readings (heart rate, respiratory rate, wrist temperature, blood oxygen where supported, sleep duration) together, with a band of values typical for you and a flag when one or more is outside that band on a given night.

Sensor-to-model matrix

A quick reference for which sensor is on which current model:

Where regional availability matters

A handful of Apple Watch health features are gated by where you are, not just which model you bought. The current picture, sourced from Apple's per-feature support pages and the watchOS feature availability page:

Where a feature isn't available in a given country, Apple either greys it out in the Health app setup or doesn't expose the setup option at all.

The line between wellness signal and medical reading

Apple is unusually disciplined about the language it uses for its own watch features. It is worth understanding the line because it is also the line that the European MDR, the German HWG and the equivalent rules in other jurisdictions draw.

The pattern in Apple's own copy:

• The watch "notifies" you of patterns over 30 days. It does not "diagnose."
• Features are framed as "insights" or "possible signs." Not "detection of disease."
• Each notification carries an explicit disclaimer that it is not intended to diagnose, treat or aid in the management of the condition it relates to. The Hypertension Notifications support page adds: "Apple Watch cannot detect heart attacks."
• The Blood Oxygen app is labelled as for "general fitness and wellness purposes" only.

The corollary for readers: Apple Watch readings are useful as a personal baseline and as a trigger to talk to a clinician. They are not a substitute for a clinical measurement when one is indicated, and a clinician who needs a reading taken under controlled conditions will take one themselves.

Where Sam Health fits in

Sam Health is a wellness companion app that reads your Apple Watch data via HealthKit and turns it into insights. It does not add sensors to the Apple Watch and it does not make medical claims. Where the Apple Watch shows you nightly numbers, Sam helps you understand the patterns those numbers form over weeks — your heart rate variability trend, your wrist temperature deviation pattern, how your resting heart rate changes when you sleep less.

Sam Health is a wellness app, not a medical device. Consult a healthcare professional for medical advice.

Try Sam Health

Sources

• Apple. Introducing Apple Watch Ultra 3. Press release, 9 September 2025. https://www.apple.com/newsroom/2025/09/introducing-apple-watch-ultra-3/ — accessed 15 May 2026.
• Apple. Apple introduces Apple Watch SE 3. Press release, 9 September 2025. https://www.apple.com/newsroom/2025/09/apple-introduces-apple-watch-se-3/ — accessed 15 May 2026.
• Apple. Apple debuts Apple Watch Series 11, featuring groundbreaking health insights. Press release, 9 September 2025. https://www.apple.com/newsroom/2025/09/apple-debuts-apple-watch-series-11-featuring-groundbreaking-health-insights/ — accessed 15 May 2026.
• Apple. An update on Blood Oxygen for Apple Watch in the U.S. Press release, August 2025. https://www.apple.com/newsroom/2025/08/an-update-on-blood-oxygen-for-apple-watch-in-the-us/ — accessed 15 May 2026.
• Apple Support. Take an ECG with the ECG app on Apple Watch. https://support.apple.com/en-us/120278 — accessed 15 May 2026.
• Apple Support. How to use the Blood Oxygen app on Apple Watch. Published 15 September 2025. https://support.apple.com/en-us/120358 — accessed 15 May 2026.
• Apple Support. Track your nightly wrist temperature changes with Apple Watch. https://support.apple.com/en-us/102674 — accessed 15 May 2026.
• Apple Support. Sleep apnea notifications on your Apple Watch. Published 18 September 2025. https://support.apple.com/en-us/120031 — accessed 15 May 2026.
• Apple Support. Hypertension notifications on your Apple Watch. Published 19 September 2025. https://support.apple.com/en-us/117296 — accessed 15 May 2026.
• Apple Developer. heartRateVariabilitySDNN — HKQuantityTypeIdentifier. https://developer.apple.com/documentation/healthkit/hkquantitytypeidentifier/heartratevariabilitysdnn — accessed 15 May 2026.
• Apple. Apple Watch compare. https://www.apple.com/watch/compare/ — accessed 15 May 2026.
• Apple. watchOS feature availability. https://www.apple.com/watchos/feature-availability/ — accessed 15 May 2026.