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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

Oura Ring 5

Silver finish, whole sizes 6 to 13, plus Oura Membership

$399US price, checked Oct 23, 2026

Compact titanium sleep ring that needs a paid membership

Check price at Oura Full review →

Criterion	Circular Ring 2	Oura Ring 5
US price	$349Checked Oct 24, 2026 · Price details in the review	$399Checked Oct 23, 2026 · Price details in the review
Three-year ownership estimate	$349 Incomplete known subtotal. Not included: energy use.	$608.97 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 6 to 13, want sleep staging and readiness scores without a wrist device, and will keep paying for membership.
Main trade-off	Circular publishes no accuracy data for its blood pressure estimate and names no maker for its FDA-cleared algorithm.	Without a membership the app shows only three daily scores, and Ring 5 stores three days of data, compared with seven on Ring 4.
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: 6 to 9 days, depending on ring size and usage. A full charge takes about 80 minutes, depending on battery level Sensors: Red, green and infrared LEDs with 2 photodetectors, plus a temperature sensor and an accelerometer Membership: $5.99 a month or $69.99 a year (US, before tax). New members get the first month included, but adding a ring to an existing account doesn't add another free month Sizes: Whole sizes 6 to 13 only. Oura recommends the Ring 5 sizing kit first, since Ring 4 sizing differs Water resistance: 100 m (328 ft), IP68. Oura says it's not for diving On-ring data storage: Up to 3 days (up to 7 days on Ring 4) Compatibility: iOS and Android, over Bluetooth 5.0
Exact variant	Obsidian Black finish, US sizes 6 to 14 (or the $5 sizing kit option), charging case included	Silver finish, whole sizes 6 to 13, plus Oura Membership
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.	6.09 mm wide and 2.28 mm thick, with a 0.7 mm sensor dome. Weight starts at 2 g, depending on ring size.
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. Oura recommends the Ring 5 sizing kit to choose your size, worn for at least 24 hours first. You can order without a kit if you already have one, or choose 'Size later', which includes a free kit. Oura says the index finger gives the best accuracy. Then pair the ring with the Oura App on iOS or Android.
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 inner and outer surfaces are titanium, and the inside has no seams. Oura says every finish has a super-hard PVD coating for scratch resistance. This review covers the Silver finish.
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 1-year protection plan comes with the ring. The Silver product page offers upgrades to 2 years for $45 or 3 years for $60. The product page doesn't say what the plan covers, such as battery wear, scratches or loss. Oura's return FAQ says warranty replacements can't be returned or refunded.
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.	Oura's general Return & Exchange FAQs let you return an order within 30 days of receiving it, if the items are fully functional and undamaged. A ring set has to come back with the ring, charger and USB-C cable. Each item can be returned or exchanged once, and ring exchanges are only for a different size of the same ring. Refunds go to the original payment method, but original shipping, handling and customs fees aren't refunded. Rings bought from other retailers go back through that retailer. Oura says to cancel the membership in the app or Membership Hub when you return a ring, so the charges don't continue.
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	What the included 1-year protection plan covers, such as battery wear, scratches or loss The Charging Case's price Whether the two-photodetector design changes heart-rate or sleep-staging accuracy compared with Ring 4 How accurate the ring itself is: the studies behind Oura's accuracy figures were published in 2020 and 2021, before Ring 5 Battery lifespan and replacement options The charger's power draw

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.