The most ambitious smart ring on paper — on-finger ECG, AFib detection and an AI coach, all subscription-free — but the software is unfinished, and the headline health features didn’t reliably work in independent testing.
Best for early adopters excited by on-ring ECG/AFib and AI coaching who accept that the software is unfinished. Everyone else should wait for it to mature.
The Circular Ring 2 is the boldest hardware pitch in the category: the first smart ring with an on-finger ECG sensor and atrial-fibrillation (AFib) detection, paired with "Kira," a subscription-free AI coach that reads 140+ biometric markers after a 14-day calibration. On paper it combines ECG + AFib + proactive AI + zero subscription in a way no other ring does. In practice, independent 2026 reviews found the software got in the way — the ECG and AFib monitoring never fully worked during testing, and promised blood-pressure and glucose features had not arrived. Battery is about six days. It’s a genuinely innovative ring whose ambition currently outruns its execution.
How we tested: Evidence-based assessment — scored from Circular specifications and independent 2026 reviews, which flagged significant software problems. Not hands-on tested by ONDA.
HRV tracking is present, but overall data reliability was uneven in independent testing.
Sensor and signal quality
7.5
The most ambitious sensor array in a ring — on-finger ECG and AFib detection. The hardware is real; the problem is the software driving it.
Sleep tracking accuracy
6.5
Standard sleep tracking, undercut by the app’s overall roughness.
Data access and export
6.0
Data lives in the Circular app with the Kira AI layer; no truly open API.
Wearability and battery
6.5
About six days of battery (eight claimed); comfortable to wear, in multiple finishes.
App and software experience
5.5
The weak point. Independent reviewers found the software buggy and unfinished — the ECG/AFib features didn’t reliably work, and promised blood-pressure and glucose tracking hadn’t shipped.
Value
6.0
From $349 (higher finishes cost more), subscription-free. Fair only if you’re buying the potential — the marquee features don’t yet fully deliver.
Pros
+First smart ring with on-finger ECG and AFib detection
+Subscription-free, including the Kira AI coach
+Genuinely innovative hardware ambition
+Multiple finishes; ~6-day battery
Cons
−ECG/AFib monitoring did not reliably work in independent testing
−Buggy, unfinished software
−Promised blood-pressure and glucose features not yet shipped
No other smart ring is this ambitious. The Circular Ring 2 puts an ECG sensor on your finger with atrial-fibrillation detection — a first for the category — and pairs it with "Kira," a subscription-free AI coach that reads 140+ biometric markers and personalises after a 14-day calibration. The combination of ECG, AFib, a proactive AI and no subscription genuinely doesn’t exist elsewhere.
Where it falls short
Execution. Independent 2026 reviews were clear: the software got in the way. The headline ECG and AFib monitoring never fully worked during testing, and promised blood-pressure and glucose features had not arrived. For a ring whose entire pitch is advanced heart-rhythm sensing, features that don’t reliably work are a serious problem, not a footnote.
Who it is for
Choose the Circular Ring 2 only if you’re an early adopter who wants on-ring ECG/AFib and AI coaching and accepts buying the potential rather than a finished product. If you want features that work today, the RingConn Gen 3 (subscription-free, with vascular and sleep-apnea insights that ship) or Oura Ring 5 are safer.
