Heart rate monitors are part and parcel of smartwatches and fitness trackers now, but electrocardiogram (ECG) is the new key 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.
Essential reading: How to use the Apple Watch ECG feature
What is ECG and why is it a useful feature to have on a smartwatch? We get into all of the key details below.
Update: This article was updated in August 2020 to add details of the new Fitbit Sense with ECG.
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, itâs captured by the sensors. The algorithm then gets to work to produce heart rate data.
But itâs not as accurate as it could be â especially where medical issues are involved.
Enter the electrocardiogram (ECG or EKG). Rather than measuring blood flow, itâs designed to measure how well your heart is working.
Itâs a term youâd more commonly hear in the medical industry, referring to an electrocardiograph that's used to detect any cardiac abnormalities.
Which smartwatches have ECG?
The list of smartwatches that currently include an ECG are the following:
- Apple Watch Series 4
- Apple Watch Series 5
- Samsung Galaxy Watch Active 2
- Samsung Galaxy Watch 3
- Fitbit Sense
- Withings ScanWatch
- Withings Move ECG
- Amazfit Smartwatch 2
How does ECG technology 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 â and determine if there are any abnormalities.
âIn 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,â 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.
For example, rather than place electrodes on your skin, the Apple Watch example requires you to hold your finger on the deviceâs digital crown. Wait for 30 seconds and the electrical activity of your heart draws a red trace across the watchâs screen. Once youâre 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, signs that you might have atrial fibrillation or an inconclusive reading.
Samsung's ECG-packing smartwatches uses its 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 â the single lead is taking one.
That means a single lead ECG has limited capabilities and offers a single view of your heart. It canât be relied upon to detect all heart rhythm abnormalities â or worsening heart problems. It also canât be relied upon to detect the electrical changes that take place during a heart attack or abnormal heart structure.
Apple makes this clear, but itâs 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?
An ECG carried out by a medical professional can identify many issues with your heart. But ECG devices designed to be used at home arenât 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, including the problems that they can identify and the others they might be able to.
Atrial fibrillation is a heart condition that can cause an irregular and abnormally fast heartbeat. Itâs 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 Appleâs 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. âIrregularities in heart rate can be episodic, and difficult to capture,â explains Dr Grimes, âSo a personal ECG that you carry with you can help clinicians record when palpitations happen and help with diagnosis.â
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 youâre 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 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 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.
âIndividuals may be given a mobile ECG device by their health professional if they are concerned they may have paroxysmal Atrial fibrillation â thatâs 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.â
Abnormal heart rhythms (arrythmia)
Neither the Apple Watch 4 or the KardiaBand are cleared to detect other kinds of abnormal heart rhythm, but that doesnât mean they arenât 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 that could lead to fainting and sudden death.
âIn July 2018, AliveCor announced a collaboration with Mayo Clinic to develop tools to facilitate screening for LQTS,â an AliveCor spokesperson says. âAlthough this feature hasnât yet been commercialised, itâs a promising step toward detecting this deadly disorder before itâs too late.â
Like Atrial fibrillation, one of the reasons personal ECG devices lend themselves to detecting a condition like LQTS is that itâs often brought on through exercise and stress. That means even if youâve had an ECG with a professional it might not have been detected. But being able to take a reading when youâre out and about, at the gym or exercising could be a life-saver.
An ST-elevation myocardial infarction (STEMI) is a serious heart attack that occurs when one of the heartâs major arteries is blocked.
Like LQTS, thereâs no official word that personal ECG devices can detect a heart attack. But that doesnât mean AliveCor isnât using its technology to try.
âIn November 2018, findings from the STLEUIS International Multicenter Study suggest that a research version of AliveCorâs ECG technology is capable of identifying STEMI,â 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.
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.
The problems with false positives â and negatives
ECG devices available to consumers can detect a range of heart problems, whether theyâve been cleared to or not, but that doesnât mean they should replace a trip to your doctor.
âReading an ECG is tricky,â Dr Grimes explains. âCurrent 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.â
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 donât. Dr Grimes calls these âfalse negativesâ and âfalse positivesâ.
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 â but itâs best to head to a medical professional if you see a reading youâre concerned about, to get it checked out.
ECG wearables available right now
Apple Watch Series 5
The latest Apple Watch uses ECG, with sensors built into the ceramic heart rate monitor under the watch, and also the new Digital Crown.
Fire up the ECO 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 a 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 Are with more than 20 countries now able to make use of the health feature.
Check out our Apple Watch Series 5 review.
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, hold 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 feature is in final review with the FDA for approval for use in the US, and the company confirmed to Wareable that it would be approved "this side of the Holidays".
Check out our full guide to Fitbit Sense.
Samsung Galaxy Watch 3
The Galaxy Watch 3 is the second Samsung smartwatch to include an ECG.
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.
Currently, Samsung's Health Monitor app has received clearance in its native Korea and has now received clearance in the US for its feature to being getting to serious monitoring work.
Have a read of our full Samsung Galaxy Watch 3 review.
Samsung Galaxy Watch Active 2
The Watch Active 2 was the first Samsung smartwatch to pack an ECG and takes that reading just like described on the Galaxy Watch 3.
That ECG feature has currently only been approved in Korea, though the recent FDA clearance for the Galaxy Watch 3 may suggest the same clearance could soon be applied to its cheaper, smaller smartwatch.
Check out our Samsung Galaxy Watch Active 2 review.
Withings Move ECG
Price when reviewed: ÂŁ129.95
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.
Read our full Withings Move ECG review.
Announced at CES 2020 and also awaiting FDA approval, the 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 also 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.
The ScanWatch looks like it's ready for release in the EU, but we wouldn't hold your breath for a US release anytime soon.
Check out our first impressions of the Withings ScanWatch.
Amazfit Verge 2
From around ÂŁ115
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.
Price: ÂŁ449, getqardio.com
Qardio's wearable takes the form of a chest strap and uses medical-grade ECG tech that can send live data on your heart rate, heart rate variability, respiratory rate, temperature and activity to your phone.
Like AliveCor's Apple Watch strap, the QardioCore is designed as a preventative, everyday (or week) health monitoring device to be used at home in between checkups.
It's currently only available to buy in Canada, Europe and Australia, as Qardio seeks approval from the FDA to ship in the US.
Hexoskin's new gen connected garments are equipped with ECG tech that the startup says has been clinically validated to continuously track heartbeats. The iOS and Android compatible clothing can additionally take heart rate variability measurements to offer insights into stress, training effort, training load and fatigue.