Irregular rhythm notifications, explained
Your watch can check your pulse for signs of AFib in the background. Here is how that works, how it differs from the ECG app and AFib History, and which watches have each one.
From Dr. Kenny Civello, cardiologist and electrophysiologist
An irregular rhythm notification comes from the light sensor on the back of your watch. Now and then, while you sit still, it times the gap between pulses. If the gaps keep coming out uneven, you get an alert. It is a reason to record an ECG and talk with a doctor. It is not a diagnosis.
It checks while you are still
Movement scrambles the pulse signal. So the watch takes its readings when you are resting, and sometimes while you sleep.
It needs repeat readings
One uneven reading is not enough. The watch looks again, and alerts only when several readings in a row look irregular.
It is for people without AFib
It is meant for adults 22 and older who have not been told they have AFib. If you already have AFib, other tools fit better.
If an alert comes with fainting, chest pain, shortness of breath, or any other symptom that worries you, call 911. Do not wait to see what your watch says next.
How each brand decides to alert
Apple Watch checks every few hours while you are still. After one irregular reading it checks more often, and it alerts when 5 of 6 readings in a row look irregular within 48 hours. Fitbit and Pixel Watch alert after 11 irregular 5 minute readings in a row, while you are still or asleep. Samsung checks a few times a day while you are still, and alerts after about an hour of an irregular rhythm. All of them can miss AFib that is short or that happens while you are moving.
Three features that sound alike
Your watch may have one, two, or all three. They do different jobs.
| Irregular rhythm notification | ECG app | AFib History | |
|---|---|---|---|
| Sensor | Light sensor reads your pulse | Electrodes record your heart's electrical signal | Light sensor reads your pulse |
| When | In the background, now and then | Only when you start it, for 30 seconds | In the background, all week |
| What you get | An alert that your pulse looked irregular | A tracing a doctor can read, plus a label like sinus rhythm or AFib | A weekly estimate of how much time you spent in AFib |
| Who it is for | Adults with no AFib diagnosis | Adults, with or without AFib | Adults already diagnosed with AFib |
More on AFib History
AFib History is an Apple Watch feature for people a doctor has diagnosed with AFib. It shows the share of time your watch saw signs of AFib each week, down to 2 percent or less. You need to wear the watch at least 12 hours a day, 5 days a week. It does not alert you during an episode, and turning it on turns off irregular rhythm notifications. The FDA has accepted it as a tool for measuring AFib in studies of ablation devices. It can help us see whether treatment is working. Ask us before you rely on it.
What does my watch have?
Pick your watch. Features can depend on the model, your phone, and your country.
How well it works
Two very large studies tested these alerts in everyday people.
Apple Heart Study
About 419,000 people took part. About 1 in 200 got a notification. When a notification came while people wore a heart monitor patch, the patch showed AFib 84 percent of the time.
Fitbit Heart Study
About 456,000 people took part. About 1 in 100 got a notification. When a notification came during patch wear, the patch confirmed AFib 98 percent of the time.
What that means for you
When these alerts fire, they are usually right that something is irregular. But a quiet watch does not prove your rhythm is normal, and only an ECG read by a doctor can confirm AFib.
Why a doctor still needs an ECG
Current heart rhythm guidelines say AFib should be diagnosed by a clinician reading an ECG, whatever device recorded it. A pulse reading only shows the timing of each beat. Extra beats and other rhythms can look uneven too. An ECG shows the electrical pattern that tells them apart.
Why it says unavailable or shows no data
Common reasons the notifications are off or quiet.
Your age in the Health app
These features are for adults 22 and older. If the birth date in your health profile is missing or makes you younger, the feature stays off.
AFib History is on
On Apple Watch, turning on AFib History turns off irregular rhythm notifications. That is by design.
Low Power Mode
Low Power Mode stops background heart checks on Apple Watch.
Your country or phone
Some features are not offered in every country. Samsung's heart features need a Samsung Galaxy phone.
Software
Update your phone and watch. Older versions may not support the feature.
No data
The watch only takes readings when you are still and the band is snug. If you wear it loose or take it off often, there may be little to show.
Common questions
I got a notification. What now?
Record an ECG if your watch can, save it, and tell us. The My watch says I have AFib guide walks through the next steps.
No alerts means I do not have AFib, right?
No. The watch only checks now and then, mostly when you are still. It can miss short episodes. If you feel a racing or irregular heartbeat, record an ECG right then.
I already have AFib. Should I keep notifications on?
They were not built for you, and they may alert often. The ECG app, and AFib History on Apple Watch, are more useful. Ask us which to use.
Should I buy a watch to screen myself for AFib?
Studies that screened large groups with watches found few new cases. A watch is most useful if you have symptoms, risk factors, or AFib we are watching. If you want one, pick a model with an FDA cleared ECG app. See Best smartwatch for catching AFib.
Does Garmin have irregular rhythm notifications?
Garmin has an FDA cleared ECG app on some models, but not a background irregular rhythm notification. Its heart rate alerts only watch for a rate above or below a limit you set.
More on wearables
My watch says I have AFibMy watch ECG says inconclusiveMy watch says my heart rate is high or lowMy watch says I may have sleep apneaFDA cleared or wellness: what the label meansWhich wearable features are FDA clearedHow I choose the wearables I recommendFind the right wearableBest smartwatch for catching AFibBest smart ring for sleepBest home blood pressure monitorBest personal ECG without a smartwatchBest wearable for an older parentBest wearable for athletesBest wearable without a screenMore on atrial fibrillation
Lowering your AFib riskHow AFib is treatedGetting ready for your ablationThis page is general education for my patients. It does not replace advice from your own doctor. Watch notifications and ECG apps are not a diagnosis. Device names are trademarks of their makers. This page is not affiliated with any of them.
Based on: Joglar JA, et al. 2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation. Circulation. 2024. Perez MV, et al. Large-scale assessment of a smartwatch to identify atrial fibrillation (Apple Heart Study). N Engl J Med. 2019. Lubitz SA, et al. Detection of atrial fibrillation in a large population using wearable devices: the Fitbit Heart Study. Circulation. 2022.