Circular Ring 2: Only Smart Ring with Built-In ECG and FDA-Cleared AFib Detection

The only smart ring with physical ECG electrodes and FDA-cleared atrial fibrillation detection, tracking over 140 biometric markers including heart rate every 2 minutes, HRV, SpO2, sleep staging, and stress, with planned blood pressure and glucose monitoring updates, all subscription-free at $380 to $549.

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The smart ring category has evolved rapidly from simple sleep and activity trackers to sophisticated health monitoring platforms, but one clinical capability has remained exclusive to smartwatches: electrocardiogram recording. ECG on the wrist (pioneered by Apple Watch and Samsung Galaxy Watch) requires physical contact between electrodes on the watch back and a finger touching the watch crown, enabling a single-lead ECG recording that can detect atrial fibrillation. A 2022 systematic review and meta-analysis published in the European Heart Journal by Perez et al. found that consumer wearable-based AFib detection demonstrates high sensitivity (94 to 98%) and specificity (92 to 97%) compared to clinical reference standards, establishing consumer ECG as a clinically meaningful screening tool (DOI: 10.1093/eurheartj/ehac009).

The Circular Ring 2, launched in August 2025, brings ECG recording and FDA-cleared atrial fibrillation detection to the smart ring form factor for the first time, combining medical-grade cardiac monitoring with comprehensive health tracking across 140+ biometric markers in a subscription-free package.

What Is the Circular Ring 2?

The Circular Ring 2 is a health monitoring smart ring manufactured by Circular that integrates physical ECG electrodes for on-demand electrocardiogram recording and FDA-cleared atrial fibrillation detection. The ring tracks over 140 biometric markers including heart rate (measured every 2 minutes, approximately five times more frequently than typical wearables), heart rate variability, blood oxygen saturation (SpO2), skin temperature, sleep stages, stress levels, activity metrics (steps, distance, calories), and respiratory indicators.

The ECG capability uses physical electrodes embedded in the ring band. To record an ECG, the user touches the ring’s outer electrode with a finger from the opposite hand, completing the electrical circuit needed for a single-lead ECG recording. The FDA-cleared AFib detection algorithm analyzes the ECG waveform for irregular rhythm patterns characteristic of atrial fibrillation, the most common cardiac arrhythmia and a significant risk factor for stroke.

The Circular Ring 2 requires no subscription for any feature, including ECG, AFib detection, sleep analytics, and all 140+ biometric markers. This subscription-free model extends to announced future features including blood pressure estimation (planned for late 2025/2026) and blood glucose monitoring (planned for 2026).

The Science Behind Ring-Based ECG

A single-lead electrocardiogram records the electrical activity of the heart from a single vector, capturing the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization). While clinical 12-lead ECGs provide comprehensive cardiac electrical mapping, a single-lead recording is sufficient for detecting atrial fibrillation, which manifests as absent P waves and irregularly irregular R-R intervals.

Ring-based ECG recording benefits from the finger’s proximity to high-conductivity tissue and the hand’s relatively low motion artifact during recording. The finger-to-finger electrode configuration (one hand wearing the ring, the other hand touching it) creates a signal pathway through the thorax that captures cardiac electrical activity with sufficient fidelity for rhythm analysis.

Atrial fibrillation affects approximately 6 million Americans and is a leading cause of stroke. Many AFib episodes are paroxysmal (intermittent), making them difficult to detect during brief clinical encounters. A continuously worn device that can record ECG on demand whenever the user experiences symptoms (palpitations, dizziness, shortness of breath) increases the probability of capturing arrhythmia events that clinical visits miss.

What the Circular Ring 2 Does Well

The ECG with FDA-cleared AFib detection is the Circular Ring 2’s definitive differentiator. No other smart ring offers this capability, making it the only ring-form-factor option for users who want cardiac rhythm monitoring without wearing a smartwatch. For individuals at elevated AFib risk (age over 65, history of hypertension, heart failure, or previous cardiac events), having ECG capability in an always-worn ring provides a screening tool that is available whenever symptoms occur.

The 140+ biometric markers tracked from a single device create one of the most comprehensive health monitoring profiles available in any consumer wearable form factor. The heart rate measurement frequency (every 2 minutes) is notably higher than most competing rings and enables more granular cardiovascular trend analysis.

The subscription-free model for all features, including medical-grade ECG and planned future capabilities like blood pressure, makes the Circular Ring 2 a strong value proposition despite its higher upfront cost relative to some competitors.

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The planned roadmap for blood pressure and blood glucose monitoring, if delivered with acceptable accuracy, would make the Circular Ring 2 the most clinically comprehensive consumer wearable in any form factor.

Pricing, Access, and Practical Realities

The Circular Ring 2 is priced at $380 to $549 depending on the finish and material, available through Circular’s website. No subscription is required for any feature. The ring launched in August 2025.

For comparison, the Oura Ring 4 costs $349 + $6/month subscription (no ECG). The Samsung Galaxy Ring costs $399 (no ECG). The Apple Watch Series 10 ($399+) offers ECG but in a watch form factor.

Battery life is competitive with other smart rings in the category. The ring is water-resistant for daily wear including handwashing and brief water exposure.

Who It Is Best For

The Circular Ring 2 is best suited for individuals who want cardiac rhythm monitoring in a ring form factor, particularly those at elevated AFib risk who want screening capability available at all times. Adults over 65, individuals with hypertension or heart failure, and anyone who has experienced unexplained palpitations gain a screening tool that can capture ECG recordings during symptomatic episodes.

Health enthusiasts who want the most comprehensive biometric monitoring available in a smart ring will find the 140+ marker tracking and high-frequency heart rate measurement appealing.

Users who prefer rings over watches for comfort, aesthetics, or discretion but do not want to sacrifice cardiac monitoring capability now have an option that was previously unavailable.

How It Compares

Against the Oura Ring 4 ($349 + subscription), the Circular Ring 2 adds ECG and AFib detection that Oura lacks entirely. Oura’s advantages are superior sleep tracking validation and a more mature app ecosystem. The Circular Ring 2 requires no subscription; Oura gates features behind a monthly fee.

Against the Samsung Galaxy Ring ($399), the Circular Ring 2 offers ECG capability that Samsung’s ring lacks, plus subscription-free access to all features versus Samsung’s ecosystem-dependent approach.

Against the Apple Watch (various models with ECG), the Circular Ring 2 offers the same core cardiac monitoring capability in a ring form factor that is smaller, lighter, and more discreet. Apple Watch provides a vastly broader feature set (notifications, apps, GPS, payments) but at greater size and weight.

Limitations and Open Questions

ECG recording requires the user to actively initiate a recording by touching the ring with the opposite hand, which means passive AFib detection during sleep or activities where both hands are occupied is not possible. The ring detects AFib when the user records an ECG, not continuously in the background.

The planned blood pressure and blood glucose features are ambitious but undelivered as of this writing. Ring-based blood pressure and glucose estimation face significant technical challenges, and the accuracy of these features when released will determine their clinical value.

As a newer entrant in the smart ring market, Circular has less long-term track record than Oura for app stability, algorithm updates, and customer support continuity.

What This Means for Your Health

Cardiac monitoring accessibility is a significant public health opportunity. Within Healthcare Discovery‘s Four Shadows framework, cardiovascular disease remains the leading cause of death globally, and atrial fibrillation is a major stroke risk factor that is frequently undiagnosed because of its intermittent nature. Making ECG recording available in an always-worn ring removes the barriers that prevent many at-risk individuals from screening for AFib.

Within the Five Pillars framework, cardiac health connects to Movement (exercise-induced arrhythmia detection), Sleep (nocturnal AFib patterns), and Breathwork (stress-mediated cardiac rhythm changes). The comprehensive biometric monitoring also supports Nutrition (metabolic health tracking) and Mindset (stress monitoring through HRV).

Frequently Asked Questions

What is the Circular Ring 2?
The Circular Ring 2 is the only smart ring with built-in ECG electrodes and FDA-cleared atrial fibrillation detection. It tracks 140+ biometric markers including heart rate every 2 minutes, HRV, SpO2, sleep, and stress, with no subscription required.

How much does the Circular Ring 2 cost?
$380 to $549 depending on finish and material, with no subscription fees for any feature.

Can the Circular Ring 2 detect AFib?
Yes. The ring has FDA-cleared AFib detection through its built-in ECG electrodes. Users initiate an ECG recording by touching the ring with a finger from the opposite hand.

How does it compare to Oura Ring 4?
The Circular Ring 2 adds ECG and AFib detection (which Oura lacks), tracks 140+ markers, and requires no subscription. Oura offers superior sleep tracking validation and a more mature ecosystem but charges a monthly fee and has no cardiac rhythm monitoring.

Does the Circular Ring 2 require a subscription?
No. All features, including ECG, AFib detection, sleep analytics, and all biometric markers, are included without any subscription or recurring fees.

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