Apple Watch health features: what's regulated and what's wellness

The Apple Watch has become a serious consumer health device. Several of its features have actual regulatory clearances; others are wellness-grade signals. The line between a regulated medical feature and a wellness feature is worth understanding.

ECG (Series 4 and later)#

Status: FDA-authorised in the US (De Novo pathway, granted September 2018) as an over-the-counter ECG software device; also available in the UK.

What it does: 30-second single-lead ECG via the digital crown and back sensor. Can classify the recording as sinus rhythm, atrial fibrillation, or inconclusive.

Validation: Independent studies (Tison et al., senior-authored by UCSF's Gregory Marcus) and the Apple Heart Study show reasonable sensitivity and specificity for AFib detection in users who can record a quality ECG. Specificity is high enough for clinical use as a screening tool.

Limitations:

• Single-lead: won't detect ischaemia, heart block, or many other arrhythmias
• "Inconclusive" results are common
• Not validated under 22 years old
• Pacemaker users get unreliable readings
• High-noise environments produce unreadable strips

What this means in practice: A clear "AFib" notification from Apple Watch is a meaningful clinical signal worth investigating. A clear "sinus rhythm" is reassuring. Anything in between needs clinical interpretation.

Atrial fibrillation history (notification)#

Status: FDA-authorised in the US (De Novo pathway, granted September 2018); also available in the UK.

What it does: Periodic passive checks for irregular pulse using the optical sensor. Sends notifications if irregularities suggesting AFib are detected.

Important: The notification is a flag, not a diagnosis. Confirming requires ECG (Apple Watch's own ECG feature or clinical 12-lead).

Real-world impact: The Apple Heart Study (419,297 participants) showed the notification feature identified previously undiagnosed AFib in a meaningful subset of users, particularly older users. This is one of the better-documented examples of consumer technology contributing to clinical disease detection.

Sleep apnoea notifications (Series 10 and later)#

Status: FDA-cleared in the US (510(k) K240929, September 2024); also available in the UK.

What it does: Uses accelerometer-derived breathing-disturbance patterns over nights to flag possible obstructive sleep apnoea.

Validation: Apple's submitted data showed acceptable sensitivity in identifying users with moderate-to-severe OSA. Specificity in mild OSA is lower.

Limitations:

• Flag suggests further investigation; not diagnostic
• Confirmation requires sleep study (home Type III device or PSG)
• Central sleep apnoea isn't reliably detected
• Mild OSA detection rates are lower

A notification should prompt a GP appointment, not a self-purchased CPAP. See sleep-apnea-screening.

Fall detection#

Status: Not a medical device per se; classified as safety feature.

What it does: Detects hard falls and prompts an emergency call after a delay if the user is unresponsive.

Real-world impact: Multiple confirmed cases of life-saving falls detected in elderly users. False positives occur with certain sports (especially mountain biking, skiing).

SpO2#

Status: Wellness only, not a medical-grade pulse oximeter.

What it does: Spot SpO2 measurement using the optical sensor.

Limitations: Accuracy compared to medical pulse oximeters is variable; trends within an individual are more reliable than absolute values. Pre-Series 10 in the UK, this feature is reactivated post-patent-dispute settlement in late 2024.

Don't use to: Diagnose hypoxia, manage COPD, or replace clinical pulse oximetry.

Heart rate, RHR, HRV#

Status: Wellness features; validated against ECG for many uses but not regulated as medical devices.

What's reliable:

• Resting heart rate trends
• Sleep HRV trends (uses sleep windows; less motion artefact)
• Heart rate during steady-state exercise

What's less reliable:

• HR during high-motion activities (weightlifting, sprinting)
• Stage classification on sleep
• Absolute HRV values comparable to chest straps

Sleep tracking#

Status: Wellness.

What's reasonably accurate: Sleep duration, sleep efficiency, basic wake events.

What's not: Sleep stage classification (light/deep/REM); accuracy versus PSG is moderate.

See consumer-wearable-accuracy.

What Apple Watch doesn't yet do well#

• Blood pressure: no continuous BP yet (Samsung Galaxy Watch has cuffless BP but with limitations)
• Glucose — no non-invasive glucose despite years of speculation
• Skin temperature: present in newer models for cycle tracking but limited beyond that

The bigger picture#

Apple Watch has shifted from "fitness tracker" to a device with several FDA-authorised or FDA-cleared medical features. The clinical impact is real:

• Newly diagnosed AFib in users who would otherwise have been missed
• Sleep apnoea screening reaching populations who wouldn't have asked their GP
• Fall detection in elderly users

It's also still a consumer device. The medical features are screening tools, not diagnoses. The wellness features are signals, not measurements.

What we'd actually say#

For an adult over 50, the AFib notification and ECG capabilities are genuinely useful as a screening tool. A flagged abnormality should always result in a GP appointment.

For the broader population, the sleep, activity, and HRV features are reasonable wellness signals, useful for personal tracking, not diagnostic.

The sleep apnoea notification feature in Series 10+ is a meaningful addition for the under-diagnosed OSA population.

Don't let the medical-grade features replace clinical investigation. They're starting points for clinical conversations.

When to talk to a clinician#

• AFib notification or ECG showing irregular rhythm
• Sleep apnoea notification
• Chest pain, syncope, or unexplained palpitations regardless of what the watch shows
• Fall detection triggering: investigate cause
• Persistent abnormal trends in resting heart rate or HRV