Modern smartwatches have a wide array of heart-rate monitoring features. That includes passive all-day monitoring as well as spot checks for specific metrics. Some will even alert you if your heart rate suddenly spikes when it shouldn’t. The most advanced devices also have FDA-cleared electrocardiograms that may help detect atrial fibrillation.

These are impressive features considering that, just a decade ago, smartwatches were basically pedometers. In practice, heart rate monitoring can be a helpful tool for people hoping to understand more about their bodies or measure their fitness progress over time. For instance, some athletes prefer to train in heart rate zones — which is hard to do unless you can check it in real time. There have also been several stories of people who say their smartwatches saved their lives thanks to abnormal heart rate alerts.

That said, it’s important to remember that these aren’t medical devices. At the end of the day, they’re not capable of diagnosing you with any sort of condition. And, even if they were, doctors are still on the fence about how to handle wearable data that consumers collect on their own.

There are nuances to how these features work and plenty of reasons why you might get inaccurate readings. First, we’ll cover how heart rate monitoring works and how to measure your heart rate. Then we’ll get into what EKG-capable smartwatches can and cannot do and how to use the EKG feature with the current crop of smartwatches.

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How optical heart rate sensors work

The vast majority of wearables use a photoplethysmography (PPG) sensor — the green LEDs you see when you flip the device over. The LEDs shine light into your skin; the light that’s refracted back is translated by an algorithm into heart rate data. That includes your resting heart rate but also other metrics like VO2 Max and heart rate variability.

While optical heart rate sensors have gotten better over the years, wrist-based PPG sensors still aren’t always accurate. A recent study found that these sensors didn’t work as well on darker skin or people with obesity. The wrist is also not the best place for a PPG sensor. There’s a lot of noise from your arm movements, and a company’s algorithm has to be able to effectively filter that out. That’s why you could wear the same smartwatch on each arm and still get slightly different readings.

Fit is also an important factor. It varies from smartwatch to smartwatch, but here are a few general tips for getting the most accurate data possible.

• Wear the watch about one finger length above your wrist bone
• Make sure there’s good contact between the sensor array and your skin
• Tighten the strap during exercise. You may also want to wear the device higher on the wrist.
• Wipe the sensor array clean whenever it gets dirty

Photo by Victoria Song / The Verge

Viewing heart rate and settings

Once you’ve paired your smartwatch, you should dive into the settings in your watch’s companion app. That’s where you’ll get to customize how often your watch measures your heart rate. Some watches measure heart rate continuously by default; others will measure periodically to help extend battery life.

For example, the Apple Watch measures your heart rate periodically when you’re still and while walking. It only measures continuously when you’re in a workout and for the three minutes after during recovery. You don’t have the option to change that. However, other devices like Garmin and Samsung watches may let you have more of a say. Each smartwatch maker designs their app differently, but you can usually find heart rate settings in your device’s settings or a health settings menu.

Your watch may also be capable of low and high heart rate alerts. This means you’ll get a notification if, while at rest, your heart rate goes below or above a certain threshold. So if you’re sitting still and your heart rate spikes to 120 beats per minute, you might get a notification. Many watches will let you customize the range for these alerts.

Below, we’ve outlined how to access these settings for some of the most popular devices and how to measure your heart rate.

Apple Watch

To access heart rate settings, open the Watch app and scroll down the list of installed apps to Heart. From here, you can enable a variety of health measurements:

• Toggling on Cardio Fitness Notifications will tell you when it deems your cardio fitness is low.
• Enabling Irregular Rhythm notifications means you’ll get notified if the watch identifies heart rhythms that may indicate atrial fibrillation.
• You can also set ranges for High Heart Rate and Low Heart Rate notifications. These notifications alert you when you’ve passed an abnormal threshold while you’re inactive.

Again, none of these are diagnostic features.

To measure heart rate:

• Click the digital crown to bring up your apps
• Tap the Heart app (The app features a red background with a heart on it.)
• From there, you can manually start a heart rate reading
• You can also scroll down to view your resting heart rate and walking average heart rate

Fitbit trackers and smartwatches

To access heart rate settings:

• Tap your profile icon in the upper left corner
• Scroll down to Settings
• Tap Activity & Wellness
• Tap Heart Settings
• From here, you can set customized high and low heart rate alerts, as well as heart rate zones for exercise

Here’s another method:

• Tap your profile icon in the upper left corner
• Select the device’s profile
• Tap High & Low heart rate to customize these alerts.

To view heart rate:

• From the clock face, swipe up to see current heart rate
• You can also view your rate in the Exercise app during exercise
• Certain clock faces will also feature heart rate as a complication
• You can also view in further detail from the Fitbit app dashboard

Samsung Galaxy Watches

To access heart rate settings on the Galaxy Watch 4 and Watch 4 Classic:

• Head to the Samsung Health app on your watch
• Swipe down to Settings
• Tap Measurement and select the Heart Rate section
• From here, you can select whether you want to measure continuously, periodically (once every 10 minutes while still), or manually only

Photo by Chris Welch / The Verge

On Samsung’s Tizen watches:

• Press the power button on the watch
• Head to the Samsung Health app
• Swipe to Heart Rate and scroll to the bottom of the screen
• Tap HR and stress measurement
• After that, the options should be the same as above

To set up high / low heart rate alerts:

• Head to the Samsung Health app
• Tap Heart rate
• Scroll down to HR and Stress Management or Auto HR settings
• Set your watch to measure heart rate continuously
• Tap More Options or the three dots
• Tap HR alert settings
• From here, you can customize your alerts

To manually measure heart rate:

• In the Samsung Health app, tap Heart rate
• Tap Measure

Photo by Amelia Holowaty Krales / The Verge

About EKGs

There are only a handful of smartwatches that have been cleared by the FDA to measure EKGs in the US. So even if the smartwatch you buy supports this feature, you’ll have to check whether it’s been granted regulatory clearance in your country.

Assuming it has, EKGs on smartwatches work by reading electrical signals from your heart. The smartwatch’s heart rate monitor acts as an electrode, and by touching your finger to the case / digital crown, you create a closed circuit. After a short period of time, you’ll be told whether your heart rhythm for that particular reading — and only that reading — shows a normal rhythm or signs of atrial fibrillation.

It bears repeating: no watch can give you an actual medical diagnosis. The most that you can do with this information is export it to a PDF that you can then share with your doctor. If you’ve got a clean bill of health from your doctor, you may not need to use this feature at all, and that’s perfectly fine!

You should also be aware that you may get a few inconclusive readings. There are several reasons why that can happen. First, you generally have to remain very still to take these EKG readings — if you’re fidgety, that could result in an inconclusive result. Likewise, your skin might be a little wet, and that can screw up a reading.

Each smartwatch maker will have its own suggestions for how to troubleshoot, but the gist is to relax and keep still while using the EKG feature.

Apple Watch

You can only take EKGs on the Apple Watch Series 4, 5, 6, and 7.

How to get started:

• Open the Health app on your phone and follow the prompts, or tap Browse > Heart > Electrocardiograms > Set Up ECG app
• You should then see the EKG app on your watch
• Tap the EKG app on your wrist
• Touch the Digital crown with a finger from your opposite hand
• Wait 30 seconds for the watch to take a reading

To export your results:

• Open the Health app
• Tap Browse > Heart > Electrocardiograms
• From there, you should see a list of your readings
• Tap the one you want to generate a report for
• Tap Export a PDF for your doctor
• You can also tap the Share button to print or email the PDF, as well as upload it to services like Dropbox

Samsung Galaxy Watch

Only the Samsung Galaxy Watch Active 2, Galaxy Watch 3, and Galaxy Watch 4 support EKG readings.

How to get started:

• First, make sure your watch and phone are on the latest software
• Open the Samsung Health Monitor app on your watch
• Tap Download App. This should bring up the app download page on your phone.
• Tap Install
• Launch the Samsung Health Monitor app
• Tap continue and fill out information prompts
• Tap Finish. You should see a button that says Get Started.
• You’ll then have to follow some more onscreen prompts
• Select which wrist you’ll wear the watch on
• Hit Done
• You should now be able to take an EKG on your watch

To export your results:

• Open the Samsung Health Monitor app on your phone
• Tap ECG and select View History
• Select the report you want to export
• Tap Share This Report
• Select the format you’d like to send (PDF, email, etc.)

Fitbit Sense and Charge 5

Only the Fitbit Sense and Charge 5 can take ECG readings at this time.

The ECG app should already be on your watch or tracker, but if not, here’s how to install (or uninstall) the app:

• Tap your profile icon in the upper left corner
• Select device profile
• Tap Gallery
• You should see the High/Low heart rate app and the EKG app
• Tap the app icon to install / uninstall

How to get started:

• Head to the Discover tab in the Fitbit app
• Scroll down to Assessments & Reports
• Select Heart Rhythm Assessment
• Read through the educational materials
• Open the ECG app on your watch or tracker.
• Place your finger and thumb on the edges of the case
• Wait 30 seconds and then view your results

To export your results:

• Tap the Discover tab in the Fitbit app
• Scroll down to Assessments & Reports
• Select Heart Rhythm Assessment
• Tap View Results
• Select which one you want to generate a report for
• Tap Export a PDF for your doctor

Withings ScanWatch

While Withings has multiple EKG-capable watches, only the ScanWatch is cleared for use in the US.

How to get started:

• Open the Health Mate app
• Select Devices, then ScanWatch
• Tap More Settings, and then ECG
• Select which wrist you’re wearing the watch on
• On your watch, use the side button to scroll to ECG Mode
• Press the side button
• Place your fingers on the top ring for 30 seconds

To export your results:

• Your results should automatically appear in your Health Mate app feed
• Tap your results
• Scroll down to Share a Health Report and follow the prompts to create a PDF