ECG smartwatches explained: How they work and the best on the market

Updated: What you need to know about technology for serious health tracking
ECG smartwatches explained
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Heart rate monitors are part and parcel of smartwatches and fitness trackers now, but electrocardiogram (ECG/EKG) is the new sensor in town.

The technology is designed to help people keep closer tabs on their heart health, and can even be used to help identify atrial fibrillation (Afib) a serious medical condition that is a leading cause of stroke.

ECG was thrust into the wearable spotlight via the Apple Watch Series 5. It's now finding it way into other smartwatches including the Samsung Galaxy Watch 4 and new Fitbit Sense health watch.

What is ECG and why is it a useful feature to have on a smartwatch? We get into all of the key details below.

What is ECG?

Most of the wearables on the market at the moment have optical heart rate monitors inside them. This is a monitor that uses flashing LEDs to penetrate the skin and detect blood flow. When light is reflected off the flow of blood, it’s captured by the sensors. The algorithm then gets to work to turn that into an estimation of your heart rate.

But it’s not as accurate as it could be – especially where medical issues are involved.

Enter the electrocardiogram (ECG or EKG). Rather than measuring blood flow, it’s designed to measure how well your heart is working.

It’s a term you’d more commonly hear in the medical industry, referring to an electrocardiograph that's used to detect cardiac abnormalities.

Why would I buy an ECG smartwatch?

They key question for many people is 'why buy an ECG smartwatch?'. Well, for many (dare we say most people) the feature is something you'll likely use once and then forget about. But for a large subset of people, ECG is absoutely essential.

“ECG on wearables is super high value for a small segment. It is probably going to be more advantageous to our users over 50 than 20 - 25 year olds, but we're trying to build something for everybody," Dr Conor Heneghan, Director of Research Algorithms at Fitbit told Wareable.

"Afib can come and go, as can conditions that affect the rhythm of your heart. That means having a device that can take spot readings at any time, makes it a hugely powerful health tool to have at your disposal," he said.

Which smartwatches have ECG?

Fitbit Sense showing the ECG app

The list of smartwatches that currently include an ECG are the following:

ECG wearables available right now

Apple Watch Series 4/5/6/7

Price when reviewed: $399 (40mm GPS)

Apple Watch Series 6

The latest Apple Watch Series 7 (and the Series 4/5/6) has ECG functionality, with sensors built into the ceramic heart rate monitor under the watch, and also the new Digital Crown.

Fire up the ECG app, pop your finger on the crown and you'll be guided through the reading.

You'll get a notification of whether the reading was normal or Afib, and an EKG graph of your heart rate will be logged in the Apple Health smartwatch app.

Apple has FDA approval for its ECG, as well as clearance in the European Economic Area with more than 20 countries now able to make use of the health feature.

Fitbit Sense

Price when reviewed: $329

Fitbit Sense

The Fitbit Sense is the company's first health watch, and it brings a host of new sensors including ECG.

You can perform ECG spot checks using the app on the watch. When you open the app, touch your fingers to the aluminium case and hold as instructed on the watch for an ECG to be taken.

The PPG sensor also scans for abnormal rhythms including high and low heart rate.

The Fitbit ECG sensor has gained full FDA and CE approval for use in the US and Europe.

Fitbit Charge 5

Price when reviewed: $279.99

Fitbit Charge 5

Staying with Fitbit, the company has launched the ECG feature on its new Charge 5 fitness tracker – although at the time of writing, the feature is still to land on the device.

It's the only fitness tracker form factor which can take an ECG reading – so a good option for those who don't want to wear a smartwatch.

You pinch the sides of the case to take the reading, which is delivered to the Fitbit app. You can share your results with your doctor, as well as getting immediate feedback on whether your heart rhythm is normal or Afib.

Read our full Fitbit Charge 5 review.

Samsung Galaxy Watch 4

Price when reviewed: $279.99

ECG smartwatches explained: How they work and the best on the market

The Galaxy Watch 4 is the latest Samsung smartwatch in town – and the move to Wear OS hasn't affected its ability to take an ECG measurement.

The ECG app can be found on the Galaxy Watch 4 – just as it was on the Galaxy Watch 3 and Galaxy Watch Active 2 below.

It takes a 30 second reading when you place your finger on the sensor built into the top physical button. You'll also need to remain still with your forearm resting on a flat surface.

Samsung's Health Monitor app is live in the US and South Korea and it's received clearance in Europe.

It's available in Iceland, Germany, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Hungary, Ireland, Italy, Latvia, Belgium, Lithuania, Netherlands, Greece, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Austria, and the United Kingdom.

What's more, Japan, Indonesia, UAE, Chile, India and China are all confirmed for 2021.

Have a read of our full Samsung Galaxy Watch 4 review and our guide how to take an ECG reading on Samsung smartwatches.

Samsung Galaxy Watch Active 2

Price when reviewed: $279

Samsung Galaxy Watch Active 2

The Watch Active 2 was the first Samsung smartwatch to pack an ECG, and takes that reading just as described for the Galaxy Watch 4.

It's been updated to support the feature, and like its flagship sibling, it's cleared by regulators for use in Europe, the US, South Korea as well as Chile, Indonesia, and the UAE.

Now that the Galaxy Watch 4 has been released, support for the Active 2 has been set to three years. So it's technically obsolete, but still available at some decent prices.

Check out our Samsung Galaxy Watch Active 2 review.

Withings ScanWatch

Price when reviewed: $249

Withings ScanWatch

The Withings ScanWatch offers even more sensors, with SpO2 detection of sleep apnea also on board.

You can take off-the-cuff ECG readings to check for afib, and the results can be presented in a PDF to show to your doctor.

The optical heart rate sensor that checks your heart rate throughout the day will also keep an eye out for irregular heartbeats, and if it thinks you may have them, suggest you take an ECG test.

ScanWatch has been out in the EU since 2020, and is set for a US release. That's great news, as it's an excellent health wearable – and it's heading for a much bigger audience.

Check out our Withings ScanWatch review.

Withings Move ECG

Price when reviewed: $129.95

Withings Move ECG

The first hybrid watch to feature the ability to take an electrocardiogram reading – helping detect the signs of atrial fibrillation – the Move ECG is also water resistant up to 50 meters and will automatically track your activity.

Unfortunately, this one is currently still undergoing clinical validation from the FDA in the US, though it is available in the EU already.

Read our full Withings Move ECG review.

Coros Vertix 2

Price when reviewed: $699.99

Coros Vertix 2

You may not have heard of Coros, but it's a US-based fitness wearables brand that has Garmin in its sights

The Vertix 2 is the company's new outdoors GPS watch, which offers an enormous 140 hours of GPS battery life, mapping and training insights.

But up its sleeve is an ECG sensor – but it's not used to take the same type of Afib readings as the other devices in our list. It's designed to take heart rate variability readings as a stress sensor.

Read our Coros Vertix 2 review.

Amazfit Verge 2

From around $145

Amazfit Verge 2

Amazfit's latest and greatest, the Verge 2 packs ECG technology to place it as a direct competitor for other watches on this list. This works by using Huami's Huanghan No.1 always-on AI chip.

This nifty chip features a cardiac biometrics engine to monitor your heart rate more accurately, including screening for heart arrhythmia and atrial fibrillation.

At the moment, however, the Verge 2 is only available in China, with US and European launches planned.

How does ECG smartwatch tech work?

An ECG records the tiny electrical signals that are generated by the beating of your heart under your skin, which it presents as a trace. This then allows trained professionals, machines or wearables to understand more about how your heart is functioning – and determine if there are any abnormalities.

“In the simplest sense, it can tell you the heart rate (how fast), the rhythm (how regular), the state of the conduction system and muscle tissue (heart attacks), and even the level of certain chemicals like potassium in the blood, and the effect of medication,” says Dr Keith Grimes, GP and Clinical Innovation Director at Babylon Health.

An electrocardiograph in a medical setting usually requires placing electrodes on the skin situated close to the heart, which measure electrical activity produced by the heart as it contracts. The electrical activity is sent to a receiver that records the information, and this is where the heart's rhythm can be analysed and irregularities can be detected.

But the tech inside the Apple Watch (and other ECG-reading devices you can use at home) works differently.

Apple Health ECG tracking

For example, rather than place electrodes on your skin, the Apple Watch example requires you to hold your finger on the device’s digital crown. Wait for 30 seconds and the electrical activity of your heart draws a red trace across the watch’s screen. Once you’re done, the app will let you know whether the trace captured a normal heartbeat, called a sinus rhythm, or an abnormal heart beat.

On the new Fitbit Sense, when you've opened its ECG app you'll be prompted to place your fingers on the corners of the watch's frame for the same 30 seconds to take a reading. It will then indicate whether you have a normal sinus rhythm, or whether there are signs that you might have atrial fibrillation or just an inconclusive reading.

Galaxy Watch Active 2 with ECG app - only available in S. Korea

Samsung's ECG-packing smartwatches uses their touch-sensitive button as a sensor that you'll place your finger on for 30 seconds as well. After that, it will measure your heart rate and rhythm, and classify it as sinus rhythm (normal) or AFib.

The biggest difference between an electrocardiograph at a hospital and the ECG tech in your Apple, Fitbit or Samsung smartwatch is the first is a 12 lead and the latter is a single lead. In the simplest terms, the 12 lead is taking lots of readings about your heart – the single lead is taking one.

That means a single lead ECG has limited capabilities and offers a single view of your heart. It can’t be relied upon to detect all heart rhythm abnormalities – or worsening heart problems. It also can’t be relied upon to detect the electrical changes that take place during a heart attack or abnormal heart structure.

Apple makes this clear, but it’s important to differentiate between what an ECG at the hospital can offer and what tech you use at home can offer.

How can ECG tech save your life?

Apple Watch Series 4 with ECG app on screen

An ECG carried out by a medical professional can identify many issues with your heart. But ECG devices designed to be used at home aren’t quite there yet.

Here are a few of the ways the ECG tech found in your Apple Watch or Samsung smartwatch can currently save your life though, including the problems that they can identify and the others they might be able to.

Atrial fibrillation

Atrial fibrillation is a heart condition that can cause an irregular and abnormally fast heartbeat. It’s common and potentially deadly. It's also intermittent, which makes it difficult to detect. This is the one condition that both Apple and Samsung are FDA-cleared to detect. FDA approval is still pending for Fitbit's new Sense watch to do the same.

ZDNet writer Jason Perlow was part of the early testing of Apple’s Atrial fibrillation detection, and identified a problem with his heart in 2018 thanks to the data that was collected.

The reason personal devices are effective at recognising this particular kind of arrhythmia (irregular heartbeat), and the reason Perlow cites for its effectiveness in his case, is because you can take them at any time.

Unlike getting an ECG at the hospital, you can monitor your heart throughout the day. “Irregularities in heart rate can be episodic, and difficult to capture,” explains Dr Grimes, “So a personal ECG that you carry with you can help clinicians record when palpitations happen and help with diagnosis.”

This means you can take a 30-second ECG whenever you feel symptoms and also better understand the context of what may have brought them on. For example, if you just got back from a run and you’re feeling a bit off.

Dr. Tony Faranesh, senior research scientist at Fitbit says the optimal way to identify atrial fibrillation through heart rate tracking is to screen while at rest, making sleep ideal for detection.

On Fitbit's devices, that's done by using its optical-based PPG heart rate sensor. The ECG sensor, like Apple and Samsung, is used for spot checks.

Like Apple, it seems that Fitbit won't be continually scanning for signs of Afib. Though Apple and Fitbit both use the PPG sensor to check for irregular rhythms such as high or low heart rate.

Dr. Julia Reynolds, Associate Director at Innovation Agency, tells us that the Kardia Mobile built by startup AliveCor is sometimes even prescribed to patients for this exact reason.

“Individuals may be given a mobile ECG device by their health professional if they are concerned they may have paroxysmal Atrial fibrillation – that’s when it comes and goes. That way, if they are feeling signs and symptoms, they can take their own ECG when they are experiencing symptoms.”

Abnormal heart rhythms (arrythmia)

ECG Afib warning

Neither the Apple Watch 4 or the KardiaBand are cleared to detect other kinds of abnormal heart rhythm, but that doesn’t mean they aren’t able to if you or a professional can interpret the data.

The team at AliveCor has been able to use data from the KardiaBand to detect Long QT Syndrome (LQTS), which is a condition that can cause an irregular heartbeat and could lead to fainting and sudden death.

“In July 2018, AliveCor announced a collaboration with Mayo Clinic to develop tools to facilitate screening for LQTS,” an AliveCor spokesperson says. “Although this feature hasn’t yet been commercialised, it’s a promising step toward detecting this deadly disorder before it’s too late.”

Like Atrial fibrillation, one of the reasons personal ECG devices lend themselves to detecting a condition like LQTS is that it’s often brought on through exercise and stress. That means even if you’ve had an ECG with a professional it might not have been detected. But being able to take a reading when you’re out and about, at the gym or exercising could be a life-saver.

Heart attack

An ST-elevation myocardial infarction (STEMI) is a serious heart attack that occurs when one of the heart’s major arteries is blocked.

Like LQTS, there’s no official word that personal ECG devices can detect a heart attack. But that doesn’t mean AliveCor isn’t using its technology to try.

“In November 2018, findings from the STLEUIS International Multicenter Study suggest that a research version of AliveCor’s ECG technology is capable of identifying STEMI,” a spokesperson from AliveCor told us.

The study tested a standard 12-lead ECG (like the one a medical professional would use) against a mobile ECG and the AliveCor app to find the mobile version was effective in identifying STEMI with high sensitivity in comparison to the professional test.

Healthier insights

Withings ScanWatch which was announced at CES 2020

Detecting a heart attack or atrial fibrillation could be life-saving, but ECG tech could also be useful in helping us to paint a more accurate picture of our health and fitness.

QardioCore is a chest-based ECG monitor that, unlike the Apple Watch, can be worn throughout the day collecting more than 20 million data points. Although it can also detect heart rhythm irregularities, its design makes it ideal for those who are in fitness training and need more reliable feedback when heart rate activity fluctuates.

Combined with readings about body temperature, breathing rate and stress levels, an ECG measurement can be used to find out more about your body and how it responds to exercise than ever before at home.

For those serious about athletic training, this is done through Heart Rate Variability (HRV) and a Root Mean Square of the Successive Differences (RMSDD) measurement, which identifies the time between peaks and troughs in your heartbeat and helps you to train smarter.

How often should I take an ECG reading

Provided your heart gets a normal sinus rhythm, you’re likely to only need to periodically take an ECG test, just to check everything is in order.

But if you suffer from the feeling of your heart racing, palpitations or periods of feeling unwell, then you can use the ECG app as and when you need it. And it becomes an incredibly important health tool, right on your wrist.

Fitbit’s Director of Research Algorithms, Conor Heneghan, says that means users can have a better informed conversation with your doctor.

“The problem with cardiac issues with rhythm is they're so intermittent,” said Heneghan.

“For people who have palpitations or other symptoms, ECG can be a reassurance. And if they feel like something's a bit odd going on physiologically they can capture that moment to speak with their doctor about it,” he continued.

Fitbit also recommends that the ECG feature should only be used by those aged 22 or above.

The problems with false positives – and negatives

ECG devices available to consumers can detect a range of heart problems, whether they’ve been cleared to or not, but that doesn’t mean they should replace a trip to your doctor.

“Reading an ECG is tricky,” Dr Grimes explains. “Current technology uses machine learning to detect common abnormalities, but personal ECG, like the kind you find on the Apple Watch, is not as accurate as medical devices.”

Personal ECG devices are proven to save lives, but on the flip-side they can still miss major problems or cause people to worry they have issues with their heart when they don’t. Dr Grimes calls these “false negatives” and “false positives”.

Although many in the medical profession are warning people to be wary of the results they get from their Apple Watch or other ECG device, having more control over our health at home is going to become more widespread over time.

That means instead of advising against ECG devices, people need to be informed that readings might not always be accurate – but it’s best to head to a medical professional if you see a reading you’re concerned about, to get it checked out.