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Smart ring

Circular Ring 2

Obsidian Black finish, US sizes 6 to 14 (or the $5 sizing kit option), charging case included

$349US price, checked Oct 24, 2026

Smart ring with on-demand ECG, a charging case and no mandatory subscription

Check price at Circular Full review →

Smart ring

Ultrahuman Ring PRO

Aster Black finish, whole sizes 5 to 14, with PRO Charging Case

$479US price, checked Oct 23, 2026

Subscription-free titanium ring with its charging case included

Check price at Ultrahuman Full review →

Criterion	Circular Ring 2	Ultrahuman Ring PRO
US price	$349Checked Oct 24, 2026 · Price details in the review	$479Checked Oct 23, 2026 · Price details in the review
Three-year ownership estimate	$349 Incomplete known subtotal. Not included: energy use.	$479 Incomplete known subtotal. Not included: energy use.
Choose if	You wear a US size 6 to 14 and want an on-demand ECG from a ring for $349 without a required yearly plan.	You wear a whole ring size from 5 to 14, want long battery life and would rather pay $479 once than pay a yearly membership.
Main trade-off	Circular publishes no accuracy data for its blood pressure estimate and names no maker for its FDA-cleared algorithm.	Ultrahuman publishes no accuracy figures for Ring PRO, some features are paid PowerPlugs, and theft and loss support comes only with the Max membership.
Key specifications	Battery and charging: About 8 days in power mode and about 5 days in performance mode per the spec table (the FAQ says 4 to 5). The wireless case recharges the ring in about 30 minutes. A case is included. Sensors: Single-lead ECG, optical PPG (green, red and infrared), skin temperature and a 3-axis accelerometer. Circular's science page lists the ECG at 510 Hz and the optical signal at 25 Hz. ECG and AFib: Circular says the AFib classification uses an algorithm cleared by the FDA. It names no algorithm maker or clearance number on the pages checked. You can export the trace as a PDF. Blood pressure estimate: Circular estimates blood pressure from the pulse wave timed between its ECG and optical sensors. You enter three cuff readings at setup and one every 30 days. A session takes about a minute and lands in one of six bands. Circular calls it a wellness estimate, not a diagnosis, and publishes no accuracy data. Subscription and paid features: Circular says no subscription is mandatory, and the product page says blood pressure comes included with nothing to renew. Its help center says the advanced parts of blood pressure and glucose are paid, by card or with app coins. Those parts are insights, long-term trends and PDF export. The Circular+ Guarantee add-on is $20 billed yearly. Sizes and fit: US 6 to 14, no half sizes. Sizes run about half a size above standard. A sizing kit is a $5 size option and can't be returned. Water resistance and storage: IP68, and Circular's FAQ says showers and swimming are fine. The ring stores 7 days of data and then overwrites the oldest. Circular suggests syncing every 5 to 6 days. Compatibility: iOS and Android over Bluetooth Low Energy. It syncs with Apple Health and Android Health Connect. Circular lists no minimum iOS or Android version on the pages checked. Delivery: Ships to the US with import duties and taxes prepaid (Delivered Duty Paid, per Circular's terms). Estimated delivery runs 3 to 25 days depending on method and address. Shipping and handling are included in a ring's price. US import status: Circular SAS was named in Oura's ITC case 337-TA-1398. It settled with Oura in June 2024, and the ITC ended the case against it in 2024 on that settlement. The August 2025 exclusion order covers the remaining respondents, and the cease and desist orders went only to Ultrahuman and RingConn. Oura says Circular holds a multi-year license, subject to royalties. Oura's newer ITC case, 337-TA-1468, doesn't name Circular. Next model: Circular Ring 3 comes as a Pro and a Slim. Circular says pre-orders open in January 2027 and prices come at launch. It says Ring 2 stays on sale until Ring 3 is released.	Battery life: Up to 15 days (about 12 days in Turbo Mode, 15+ days in Chill Mode). Up to 45 days between wall charges with the PRO Charging Case. About 2.5 hours for a full charge. Sensors: Temperature sensor, redesigned PPG sensor and 6-axis IMU. Dual-core processor with on-chip machine learning. Subscription: No recurring subscription fees for accessing your data. Optional PowerPlugs cost extra: Cardio Adaptability, for example, is $24 for 1 year or $38 for 2 years, and Cycle & Ovulation Pro is $39 for 1 year or $69 for 2 years. The buy page also offers an optional membership, Ultrahuman Max, at $9.99 a month or $99.99 for one year, which includes PowerPlugs and UltrahumanX coverage. Data storage: Up to 250 days of data on internal and external flash, per Ultrahuman's comparison page. Up to 1 year of ring data backed up to the PRO Charging Case. Water resistance: 100 m (328 ft) Sizes: 5 to 14, no half sizes. Weight and thickness: 3.3 to 4.8 g depending on size. 2.65 mm thick (varies by size). US import status: Allowed, with conditions. The US International Trade Commission (ITC) barred imports of Ultrahuman rings that infringe an Oura patent on August 21, 2025, after finding that Ring AIR did. In March 2026, US Customs ruled that Ring PRO's redesigned unibody ring falls outside that order. Each import needs a certification that Customs approves. Ultrahuman's US store listed Ring PRO for sale on Oct 23, 2026.
Exact variant	Obsidian Black finish, US sizes 6 to 14 (or the $5 sizing kit option), charging case included	Aster Black finish, whole sizes 5 to 14, with PRO Charging Case
Dimensions	Circular's product page lists the ring as 2.55 mm thick, 7.8 mm wide and about 4 g. Its science page gives 4.5 g and a 2.6 mm profile, so the figures differ by page. Circular doesn't state weight or inner diameter for each size.	It's 2.65 mm thick, though thickness varies by size. It weighs 3.3 to 4.8 g depending on size. Ultrahuman doesn't state band width or per-size inner diameter.
Installation	No installation. You pair the ring with the Circular app on iOS or Android over Bluetooth Low Energy. The box holds the ring, a wireless charging case, a USB-C cable and a cleaning cloth. Circular sizes run about half a size above standard ring sizes, so a standard 9 means a Circular 10. If you don't know your size, a sizing kit costs $5 as a size option. A size exchange has to happen within 14 days of delivery.	No installation. It pairs over Bluetooth (BLE 5.3) with the Ultrahuman app, which is on the App Store and Google Play. In the box are the ring, the Ring PRO Charger and a 1 m USB-C to USB-C cable. Ring PRO charges only on the PRO Charger or PRO Charging Case, not on a Ring AIR charger. Before you order, Ultrahuman offers a free sizing kit with plastic sizers in sizes 5 to 14.
Materials	The product page says titanium with a PVD finish and a hypoallergenic inside. Circular's science page describes grade-5 titanium with a diamond-like carbon coating instead. Circular doesn't name the inner material.	The ring is titanium with a PVD coating, plus epoxy and polycarbonate. Ultrahuman says the inner surface is hypoallergenic plastic and titanium. The charging case is aluminum, stainless steel and plastic.
Warranty	One year from delivery, covering defects in materials and workmanship (two years in the EU under local law). It excludes a wrong size, normal wear and tear, cosmetic damage such as scratches, accidents and misuse. Batteries are covered only if a defect damaged the product. Circular's help center says the battery can't be replaced and offers a discount code toward a new ring if it weakens. The optional Circular+ Guarantee costs $20 billed yearly, and the product page describes it only as extra protection.	A 12-month limited warranty runs from delivery and covers defects in materials and workmanship, valid only in the country of purchase. Ultrahuman's Terms of Sale exclude consumable parts such as batteries or protective coatings, unless a defect caused the failure. They also exclude accidents, misuse, normal wear and tear, and cosmetic damage unless a defect caused it. Those terms name Ring AIR, not Ring PRO, and the Ring PRO FAQ confirms only the one-year length. Ultrahuman's buy page lists UltrahumanX coverage, with accidental damage, loss and theft support, as included with the Max membership. Ultrahuman's Terms of Sale say UltrahumanX is not an insurance program. We found no standalone UltrahumanX price.
Returns	14 days from receipt, for any reason, if the ring is unused and in its original condition. You email support with a photo and your order number to start the return. For a change-of-mind return you pay shipping back, and Circular keeps a fixed $25 of shipping and handling from the refund. Import taxes aren't refunded. Sizing kits can't be returned. A size or color exchange has its own 14-day window, and you pay the shipping.	If you're not completely satisfied, you can return it within 30 days of delivery. Send it back in the original packaging with all original accessories, including the charger. The Ring PRO FAQ and the Smart Rings Terms of Sale both say return shipping is free. No restocking fee is stated. The Terms of Sale list these return terms under the Ring AIR heading, and the FAQ applies them to Ring PRO.
Unresolved questions	Which company makes the FDA-cleared AFib algorithm, and its 510(k) number Independent accuracy data for Ring 2's ECG, sleep, blood oxygen and blood pressure, since Circular's own validation work is still in review What the Circular+ Guarantee covers and what a Circular+ subscription costs Whether the advanced parts of blood pressure are paid for every buyer, since the pages disagree Whether Oura's license names Ring 2, how long it lasts and what the royalty is Battery lifespan, out-of-warranty replacement cost and charger power draw Inner diameter for each size and the minimum iOS and Android versions The ring's FCC equipment authorization, which the pages checked don't mention How long Circular will keep selling and supporting Ring 2 after Ring 3 launches	Band width and per-size inner diameter Whether a worn-out battery is repaired or replaced at a cost, since the Terms of Sale exclude battery wear from the limited warranty Independent, peer-reviewed accuracy data for Ring PRO against polysomnography or ECG Battery lifespan, out-of-warranty replacement cost and charger power draw Renewal prices for PowerPlugs after the first term The prices of PowerPlugs the buy page doesn't list, and of UltrahumanX coverage sold apart from Max Minimum supported iOS and Android versions How long Ultrahuman will sell and support Ring PRO in the US Whether a later ITC or court decision overrides the customs ruling that lets Ring PRO into the US

These comparisons use published specifications, not head-to-head tests. Prices and terms are dated. Unknown costs are not zero. Check the exact variant before you buy.