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Wearable ECG

Does your watch's irregular-heartbeat alert actually catch atrial fibrillation, and does catching it earlier actually help? Here's what the accuracy and screening research shows.

Consumer wearables now offer two related but distinct features: a single-lead ECG you can trigger yourself, and a background PPG-based algorithm that watches for an irregular pulse and alerts you when it finds one. Both are marketed around atrial fibrillation (AFib), the most common heart-rhythm disorder and a real stroke risk factor. The two questions worth separating are whether these features actually detect AFib accurately, and whether catching it this way actually changes outcomes. The evidence answers them very differently.

What your device actually calls this
Scientific measurementElectrocardiogram (electrical heart signal) or photoplethysmography (PPG, optical pulse-based irregular-rhythm detection). These are two genuinely different sensing methods, not two names for the same thing.
DeviceWhat they call itWhat it actually measures
Apple Watch"Irregular Rhythm Notification" and the "ECG app" (two separate features)The notification is PPG-based passive background monitoring; the ECG app is a genuine single-channel ECG, FDA-cleared, requires actively holding the crown. Not the same feature and don't provide the same evidence quality.
Fitbit"Fitbit ECG App" (branded the "Google ECG App" in newer materials), plus a separate passive "Irregular Heart Rhythm Notifications" featureSense 2 only. The ECG app is a genuine single-channel ECG, FDA-cleared and CE-marked, requiring an on-demand spot check. Irregular Heart Rhythm Notifications uses the same PPG sensor as everyday heart rate tracking to flag possible AFib passively, without an active check.
Samsung Galaxy Watch"Irregular Heart Rhythm Notification" and "ECG" (two separate features)FDA-cleared May 2023. Same passive/on-demand two-tier design as Apple and Fitbit; accuracy drops with motion or poor sensor contact, the same limitation every consumer ECG shares.
AmazfitOn-demand single-lead ECGA peer-reviewed evaluation reported 93.28% sensitivity and 95.35% specificity for AFib detection, a specific published figure most brands here don't have.
Withings ScanWatch"ECG"On-demand bezel-touch reading, FDA-cleared October 2021 for AFib detection specifically.

The Apple Watch's "Irregular Rhythm Notification" and "ECG app" get conflated constantly in casual conversation, but they're different tools with different evidence bases. The notification is a passive background screen; the ECG app is an actively-triggered, FDA-cleared diagnostic-adjacent recording. Fitbit's Sense 2 runs the same two-tier design. Garmin, Oura, and Whoop don't offer ECG at all: Garmin hasn't pursued single-lead certification, Oura's ring form factor has no room for the electrode setup it requires, and Whoop's band doesn't include one either.

Device measurement accuracy: Established · see the file
How each device actually shows this
Apple Watch "Irregular Rhythm Notification" and the "ECG app" (two separate features) Fitbit "Fitbit ECG App" (branded the "Google ECG App" in newer materials), plus a separate passive "Irregular Heart Rhythm Notifications" feature Samsung Galaxy Watch "Irregular Heart Rhythm Notification" and "ECG" (two separate features) Amazfit On-demand single-lead ECG Withings ScanWatch "ECG" See every device →

Sources: Apple's own support page (support.apple.com) for the two-feature distinction, primary. Fitbit/Google's own product documentation and FDA clearance materials, primary.

Research Desk · live file
See the full Wearable ECG evidence file
Every claim rated Established, Emerging, Uncertain, Insufficient, or Unsupported, with a research log reviewed against new studies on a rolling basis.
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More on Wearable ECG
Does Wearable ECG Accurately Detect Atrial Fibrillation?
I looked at what the diagnostic accuracy research actually shows about wearable ECG and AFib detection, including where the numbers hold up and where they don't.
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Does Wearable AFib Screening Actually Reduce Stroke Risk?
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Does Finding More AFib With Wearables Actually Prevent Strokes?
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GUARD-AF and the Question of Whether AFib Screening Prevents Stroke
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Does Genetic Risk Determine Who Benefits From AFib Screening?
A genetic analysis of the LOOP trial asked whether polygenic AFib risk predicts who actually benefits from screening. Here's what it found and didn't.
Do Cardiologists Agree When Reading Smartwatch ECG Strips?
A smartwatch algorithm gives one answer, but do human cardiologists agree with it, or even with each other? Here's what the interpretation research found.
Can Your Blood Pressure Cuff Catch AFib You Didn't Know You Had?
AFib detection isn't only an ECG or PPG wearable's job. Several studies have tested whether an ordinary home blood pressure monitor can screen for it too.
Can a Normal Single-Lead ECG Today Still Predict AFib Tomorrow?
The VITAL-AF trial tested whether a wearable ECG reading that isn't diagnostic today still carries a signal about AFib risk months or years later.
Is a Wrist Blood Pressure Monitor Actually Accurate?
A 2026 European Society of Hypertension consensus statement reviewed every wristwatch-type blood pressure monitor's evidence. Only two devices had real published validation.
Other metrics
Heart Rate VariabilityResting Heart RateSleepVO2 MaxWearable ECGCGMRecoveryActivityBlood Oxygen