Circular Ring 2 review: ECG on paper, no forced fee, bought direct

How this review was built

We haven't worn, owned or lab-tested a Circular Ring 2. This review is built from Circular's product, shop, home and help pages, its license with Oura, Tech Advisor's October 2025 review, and the published sleep-lab research, all linked below. On our ring rubric (how we score) it scores 6.0 out of 10, sixth of the six no-fee rings in our best smart rings without a subscription.

That low rank isn't about the fee. Circular scores 8 out of 10 on cost of ownership and 9 out of 10 on phone support. It loses its points on evidence (2 out of 10: we found no published validation of this ring), sizing (6: it runs about half a size large) and battery (6: a shorter claim than the RingConn rings and no stated charging case). Circular's US legal footing is settled: Oura granted it “a multi-year license to continue selling Circular smart rings and associated app, subject to royalty payments” on June 25, 2024 (Oura).

What you pay over three years

Circular's shop page promises “no forced subscription,” and its product page says “Every core feature is included with the ring.” Here it is against the two alternatives on this page.

For every brand's terms in one place, see do smart rings require a subscription and what a smart ring really costs over three years.

No forced subscription, and the Coins

“No forced subscription” is a narrower promise than “no subscription.” Tech Advisor's review reported that “Future features need virtual coins”: Circular Coins, which can be bought (Tech Advisor). Circular's own wording is that every core feature comes with the ring. So what you buy today works without paying again, but new features Circular adds later may cost Coins.

For a fee-averse buyer, that's a real difference from RingConn, which sells no paid tier at all, and a real improvement on Oura, where the membership gates most of what the ring measures. It's closest to Ultrahuman's model of optional paid extras. Just go in knowing that the feature list can grow in ways you pay for.

The ECG and AFib features, read carefully

Circular lists single-lead ECG and AFib detection among the Ring 2's features, something none of the other rings we cover lists. Circular's own homepage is careful about what that means: “Circular is not a diagnostic device and does not replace medical advice.” On blood pressure, it describes “A trend read from the pulse wave, calibrated against your own cuff,” and adds, “It does not replace a cuff and it is not a diagnosis” ( Circular).

Circular's homepage makes no FDA clearance claim for the ECG. We've seen third-party claims that it's FDA-cleared, but we couldn't verify any of them, so we don't repeat them. We also found no smart ring with an FDA-cleared blood pressure feature. Treat all of it as wellness information that might prompt a doctor's visit.

What the evidence says

We found no published validation study of the Circular Ring 2. Two things are easy to confuse here, so we'll head them off:

• “Circul” is not Circular. A 2025 sleep-lab study in Scientific Reports (Herberger et al.) tested Oura, SleepOn and a ring called “Circul” against polysomnography; the Circul ring had the lowest four-stage accuracy of the three, at 35.06% (Herberger et al.). That's a different product. It tells you nothing about the Circular Ring 2, good or bad.
• Amazon's “Circul Smart Ring” is also a different brand. We found no Circular Ring 2 listing on Amazon.com.

On exercise, Tech Advisor's reviewer offered a wider judgment: “I've not tested a smart ring that I really think does a good job of tracking heart rate during exercise.” That fits the published ring studies we found, which measured overnight and resting data, not workouts. The best ring study we found, Dial et al. (2025), compared Oura rings with a Polar H10 chest strap overnight; no equivalent exists for Circular. If you buy one, our test your ring against a chest strap guide is the way to find out how yours reads.

Battery, sizing and phones

Battery. Circular claims “8 days power mode, 5 days performance.” Its product page says “30 minutes to full” for charging, while its shop page said about 60 minutes when we checked, so expect somewhere in that range. No charging case is stated. Compared with the RingConn Gen 2 (10-12 days plus a case), that means more trips to the charger. Our smart ring battery life guide reads every claim with its conditions.

Sizing. US sizes 6-14, “running approximately half a size larger than standard ring sizing,” per Circular. You can print a sizing guide, or order a physical kit first (“Replica rings arrive first”) for a small extra charge. Circular's help page says “Outer-shells and sizing kits are consumables that are not refundable” ( Circular). Given the half-size quirk, the physical kit is worth it. Our smart ring sizing guide and sizing compared across brands explain why a printed chart is the riskier route.

Phones and build. Circular's homepage lists “iOS 15 and later, Android 9 and later,” which reaches older phones than RingConn's iOS 17 and Android 10 minimums. (An older help page quotes lower versions; we go with the current homepage.) It's titanium with a PVD coating and rated IP68; for what that means around water, see is a smart ring waterproof.

Buying direct: returns, warranty, HSA/FSA

The Circular Ring 2 is sold by Circular's own store, which ships worldwide. That means Circular's terms, not Amazon's:

• Returns: “14-day return no questions asked” on the shop page. The help page adds that you may return a “fully functional and undamaged” product “for any reason within 14 days of receipt of your ring for a full refund.” Fourteen days is short for a ring you'll want to sleep in for a couple of weeks, so start wearing it the day it arrives.
• Warranty: a “1-year manufacturer warranty” in the US (two years in the EU).
• HSA/FSA: Circular says the ring is eligible. See our HSA and FSA guide for the IRS rule behind it.

Because it isn't sold on Amazon, we don't earn a commission on it; the card links to Circular's store as a plain reference link. Compare every brand's terms in our warranty and returns guide.

Who should skip it

• Anyone who wants published accuracy evidence. We found none for this ring.
• Anyone buying for a medical-grade ECG. Circular says it isn't a diagnostic device, and we found no FDA clearance claim.
• Anyone who wants to buy through Amazon or needs more than 14 days to decide.
• Anyone who hates charging. 8 days at best in power mode, 5 in performance mode, and no stated case.
• Anyone who wants a promise that nothing will ever cost extra. Future features may need Circular Coins.

The alternatives

RingConn Gen 2 is the no-fee ring we'd point most Circular shoppers to: no paid tier at all, 10-12 days a charge plus a case rated at up to 150 days, a chest-strap preprint of its own, and it's on Amazon. It has no ECG feature. See the RingConn Gen 2 review.

Oura Ring 5 is the pick if evidence matters more than the fee: the best-validated lineage in the category, but most features sit behind the membership. Our Circular Ring 2 vs Oura comparison puts the two side by side, and the Oura Ring 5 review has the membership math. Every ring is in the smart ring comparison chart, and the other models are on our reviews hub.