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Are ECG Readings on Smartwatches Reliable?

Jul 28, 2025

Quick Check Before We Start

How many of these can you tick off：

I know what an ECG is and what it measures I've seen or used the ECG feature on a smartwatch I understand the difference between a hospital ECG and a watch ECG I'm know some smartwatch ECG apps are FDA-cleared I know they're mainly designed to detect atrial fibrillation (AFib) I know when an ECG result should be shared with a doctor

Many years ago, heart rate monitoring on your wrist was mostly for serious athletes or fitness enthusiasts willing to invest in specialized gear. The first wireless heart rate monitor watch appeared back in 1982, but for decades, these devices were expensive, limited in features, and not something the average person would wear every day.

That began to change as technology got smaller, cheaper, and more stylish. Smartwatches and fitness trackers with built-in heart rate sensors became affordable and widely available, putting a feature once reserved for elite training right onto millions of wrists.

Once heart rate tracking became mainstream, manufacturers started adding more advanced tools. First came SpO₂ sensors to track oxygen levels, then ECGs — once hospital-only — now built into chest straps, arm bands, and smartwatches.

And that brings us to today. You can be sitting at your desk, sipping coffee, when a gentle buzz on your wrist says, “Possible irregular rhythm detected.” In seconds, your watch has run an ECG — a test that used to mean a clinic visit, sticky pads on your chest, wires everywhere, and a printout only a cardiologist could interpret.

It’s a remarkable shift. Health tracking has moved from an occasional “check-in” at the doctor’s office to something you can monitor daily, even hourly — and now, medical-grade tests at home. But with this new convenience comes a bigger question: Are smartwatch ECGs truly reliable?

What an ECG Actually Measures

What is an ECG? You’ve probably seen a heart monitor in a movie or hospital — that wavy line moving across the screen with an occasional beep. That’s the visual form of an ECG, or EKG as it’s sometimes called. It’s a simple test that records the electrical signals controlling your heartbeat.

Every time your heart beats, a tiny electrical impulse tells it when to squeeze and when to relax. By capturing those signals, an ECG helps doctors check two key things:

Your heart rhythm — whether it’s steady, too fast, too slow, or irregular.
Clues about heart health — for example, if certain parts of the heart muscle aren’t getting enough blood.

In hospitals, ECGs are done with 12 different sensors placed in specific spots on your chest, arms, and legs. This gives doctors a complete view of how the electrical signal travels through your heart — a bit like watching a sports game from multiple camera angles instead of just one.

A smartwatch ECG works differently. It uses just one “view” — called a single lead — to pick up your heart’s electrical signal. That’s enough to spot certain rhythm problems, like atrial fibrillation, but it can miss subtler issues that need a full hospital setup to detect.

So think of a smartwatch ECG as a quick check — like taking your temperature at home when you feel unwell. It can tell you something’s off, but it can’t give the whole diagnosis.

How Smartwatch ECG Technology Works

It’s pretty wild that the same device that pings you about a text message can also read your heart’s electrical signals — but here’s how it pulls it off.

Most ECG-enabled smartwatches (Apple Watch, Samsung Galaxy Watch, Fitbit Sense, Withings ScanWatch, etc.) have two key metal contacts — one on the back of the watch that rests against your skin, and another on the bezel or crown. When you touch the second contact with your finger, you create a closed circuit from one arm, through your chest, to the other arm (or hand).

Think of it like connecting two points on a battery with a wire — your body becomes that “wire,” carrying your heart’s tiny electrical signals from one point to another. The watch’s sensors pick up these signals, then algorithms process them into that familiar wave pattern you see on-screen.

Some watches even let you save the recording as a PDF to share with your doctor. The tech is impressive — especially considering it’s packed into a device that also counts your steps, measures your sleep, and maybe even controls your Alexa.

How Reliable Are Smartwatch ECGs?

If your watch flashes “irregular rhythm detected,” should you believe it? The answer: for some conditions, yes… but with limits.

What the Research Says

Smartwatch ECGs are especially accurate for detecting atrial fibrillation (AFib) — the condition most of them are designed and approved for.

Large studies involving thousands of participants have found that popular smartwatch ECGs can detect AFib with over 90% accuracy compared to a hospital ECG.
A 2021 pooled analysis reported 100% sensitivity and 95% specificity for AFib detection, with an overall accuracy of 97% (source from JMIR).

That’s not just impressive — it can be life-changing for people who don’t know they have AFib and might only find out after a serious event like a stroke.

The Limits of a Single-Lead ECG

Your smartwatch records your heart’s electrical activity from just one angle — called a single lead. That’s enough to spot many rhythm problems, but it can miss or misinterpret others.

Ventricular tachycardia can sometimes appear normal from a single lead.
Early signs of a heart attack often require multiple views (a 12-lead ECG) to detect.
Even AFib readings can be thrown off by movement, skin resistance, or environmental interference.

Think of it like a smoke alarm — it’s great for warning you that something might be wrong, but you still need a “fire inspector” (your doctor) to confirm what’s really happening.

FDA Clearance and Why It Matters

In the U.S., some smartwatch ECG features have FDA clearance for AFib detection, meaning they’ve been clinically tested and proven to perform as well as existing approved devices for that specific purpose.

FDA-cleared smartwatch ECG apps include:

Apple Watch ECG app (Series 4 and later) – cleared in 2018
Samsung Galaxy Watch ECG – cleared in 2020
Fitbit Sense ECG app – cleared in 2020
Withings ScanWatch ECG – cleared in 2021

Why it matters:

FDA clearance means the company submitted study data showing accuracy and safety for AFib detection.
It does not mean the watch is approved for detecting other heart problems like heart attacks or rare arrhythmias.

If AFib detection is your main concern, FDA-cleared devices are the most trustworthy. But remember — they’re screening tools, not a substitute for professional diagnosis.

If your watch flags an issue — or if you have symptoms like chest pain, dizziness, or shortness of breath — don’t wait. See a doctor.

What Factors Can Affect Your Readings?

Getting a clear ECG on your watch is a lot like taking a sharp photo — you need the right conditions. Here are the main culprits that can cause inaccurate results:

Movement – Even small motions, like adjusting your glasses or shifting in your seat, can distort the signal. Stay still during the test.
Poor skin contact – Dry skin increases resistance; sweat or heavy lotion can block the signal. Keep the strap snug but comfortable.
Low battery or outdated software – Can affect how well the watch processes the reading.
Strong electronic interference – Rare, but possible if you’re near powerful machines or magnets.
Cold temperatures – Cold hands can weaken the signal your watch picks up.

Pro tip: If you get an unusual result, try again under better conditions before panicking. A single odd reading doesn’t necessarily mean trouble — but a pattern is worth sharing with your doctor.

Smartwatch ECGs: How to Use Them Wisely

Even with their limits, having ECG access right on your wrist is a huge leap forward. If you’ve ever felt your heart racing and thought, “Is this serious?” you know how valuable it is to check in the moment. A smartwatch ECG lets you capture that data instantly — and, in many cases, share it with your doctor.

For people with a history of atrial fibrillation (AFib) or those at higher risk, it can mean catching episodes early, sometimes before they lead to bigger problems. For healthy individuals, it can offer peace of mind, helping to rule out obvious rhythm issues when something feels off.

But here’s the flip side — and it doesn’t get talked about enough:

False positives: Your watch flags an irregular rhythm when nothing’s wrong, leading to unnecessary anxiety or extra medical tests.
False negatives: The reading looks fine, but you’re actually having an issue, which can delay proper care.
Over-reliance: Treating your watch like your only doctor could mean missing problems that require a full medical evaluation.

The bottom line? A smartwatch ECG is a powerful tool, not a replacement for a professional opinion. Use it as an early warning system — not the final verdict.

Best Practices for Getting the Most from Your Smartwatch ECG

Pick the right moment – Take readings when you feel unusual symptoms (like palpitations, dizziness, or shortness of breath) or at regular times if you’re tracking trends.
Stay still and comfortable – Movement can distort results. Sit down, relax, and let the watch do its job.
Interpret results responsibly – Treat “irregular rhythm” alerts as a sign to check in with your healthcare provider, not as a confirmed diagnosis.
Share the data – Most watches let you export ECGs as a PDF — send these to your doctor to add context to your symptoms.
Know when to seek urgent care – If you have chest pain, fainting, or severe shortness of breath, skip the watch and call emergency services right away.

Used wisely, a smartwatch ECG can give you valuable insight into your heart health — but only if you combine it with medical guidance and common sense.

Notes: These devices can’t replace a full medical evaluation, and they can miss or misinterpret certain heart problems. So if your watch flags something unusual, or if you have symptoms like chest pain, dizziness, or shortness of breath, don’t rely on the watch alone. Get checked out. Because at the end of the day, your smartwatch is a tool — but your health deserves the expertise of a real doctor.

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