The $349 Circular Ring 2 introduces a couple of new features to the smart ring category, but it fumbles too many basics to be a useful fitness tracker. From your finger, this stylish titanium band can take an electrocardiogram (ECG), monitor for atrial fibrillation (AFib, or a chronic irregular heartbeat), and, in a future update, let you take blood pressure readings. However, in testing, it was slow to sync, its app crashed numerous times, and its exercise and sleep metrics were often inaccurate or absent. I’ll be keeping an eye on the ambitious Circular brand to see what it does next, but I simply can't recommend the Ring 2 in its current state. Our Editors' Choice, the $349 Oura Ring 4, delivers significantly greater accuracy and offers much better overall value.

Pricing: No Subscription—At Least for Now

The Circular Ring 2 comes in black, gold, pink, or silver, with black starting at $349 and the others priced higher. Silver starts at $449, while pink and gold both cost $549. Circular doesn't charge a premium for bigger sizes within a given color.

The ring comes in sizes 6 through 14, and Circular says to wear it on your non-dominant hand and on one of your three middle fingers. The company's digital sizing feature uses your phone’s camera and AI to determine the best fit for you. The tool lets you take a picture of your hand next to a standard-size card, like a driver’s license, or you can measure a ring that already fits you well using an on-screen guide.

If you don’t want to use the digital sizing kit, the company offers a standard physical kit for an extra $5 on your order. Both the Oura Ring 4 and the Samsung Galaxy Ring ($399.99) come with free sizing kits. Samsung charges $10 for the kit initially, but discounts that cost if you proceed with a ring purchase.

While the digital sizing kit could be interpreted as Circular’s free version, the company’s FAQ page recommends the physical kit for the best accuracy, and indeed, the digital AI underestimated my size by two. I tested a size 14 in silver after using a physical sizing kit, and it fit comfortably. The digital kit recommended a size 12 for the same left index finger.

(Credit: Andrew Gebhart)

The company page also prominently states there are no subscription fees, but Circular plans to launch a premium version of its service at some point in the future alongside a couple of upcoming features. Blood pressure measurements and glucose trend monitoring, along with AI analysis of both, will be paywalled, though non-paying users will still get a general sense of their blood pressure measurements through a color-coded score without specific numbers.

Circular will take an interesting "freemium" approach to its subscription service, as you’ll be able to pay for premium membership through coins you can earn by using the app. The company hasn’t announced pricing or specifics for this service yet, so I can’t assess how viable the freemium path actually is.

For comparison, the Samsung Galaxy Ring has no premium service fees. The Oura Ring 4 requires a $5.99 monthly or $69.99 annual charge for access to most of your data.

Features: Cutting-Edge Claims, Uneven Reality

Last fall, Circular announced blood pressure and glucose measurements as upcoming features for the Ring 2, but neither has launched yet at the time of my testing. The blood pressure feature will apparently need to be calibrated with a separate cuff every month to maintain accuracy, which is exactly why I've been disappointed by similar features in devices like the Samsung Galaxy Watch 8.

Even without those capabilities, the Circular Ring 2 has a lot going for it, including FDA-approved ECG measurements and AFib monitoring, features that are not available on the company’s previous smart rings or the top competing models in the field. In another change this generation, the Ring 2 ditches the haptic feedback capabilities of older models in exchange for longer battery life.

In all, the company says the Circular Ring 2 measures more than 140 biometrics, though most fall within the standard categories for smart rings and fitness trackers. For activity and energy tracking, it measures blood oxygen saturation (SpO2), breathing rate, heart rate, heart rate variability, and skin temperature. During sleep, the Ring 2 monitors breathing, heart rhythms, oxygen intake, and sleep stages. For women, it tracks hormonal shifts and fertility.

(Credit: Andrew Gebhart)

Its companion Circular app (for Android and iOS) tabulates trends across all of your data, and features a virtual assistant named Kira for AI-powered assessments. Through the app, you can also check stress levels, take on-demand readings of your stats, and set alarms and reminders. The app even offers various guided breathing and relaxation exercises if you need help managing stress.

The Circular app doesn’t deliver as many long-term health assessments as Oura, which estimates Cardiovascular Age and Cardio Capacity (VO2 Max) over time. But in general, the amount of data Circular's ring can collect is impressive, as is its push into new territory such as AFib detection.

Design: Minimal, Durable, and Comfortable

At a glance, the Circular Ring 2 appears to be an unadorned, ordinary piece of jewelry. On closer examination, a small circle that acts as both the company logo and a placement indicator is carved in the top. Circular advises keeping the sensors opposite this logo facing down toward your palm. Those sensors are clearly visible on the interior surface when the ring is not worn. Like other popular smart rings, the Circular 2 uses red and green LEDs to collect most data. A single-lead ECG is also present.

(Credit: Andrew Gebhart)

The exterior of the ring is coated in titanium, which held up well during two weeks of testing. I wore it during multiple gym sessions and banged it against more than a few weights without any noticeable dings or dents. The hypoallergenic interior prevented skin irritation during my testing, and the sealed, waterproof design is safe for showering and swimming.

The Circular Ring 2 measures 0.10 inches thick and 0.31 inches wide, which roughly matches the dimensions of the Oura Ring 4 (0.11 and 0.31 inches). It weighs approximately 0.11 ounces, depending on the size. I don’t wear any rings when not testing a smart model, but it was comfortable enough to keep on for days at a time.

Battery Life: Close to a Week, Depending on Use

The Circular Ring 2's battery life allows it to be worn for days at a time. In testing, the Ring 2 lasted 5.5 days in Performance mode, which increases measurement frequency compared with Power mode. That result slightly beats the company's five-day battery life estimate. Circular says the battery should last 8 days in the battery-saving Power mode. It recharged to full in 46 minutes using the included case.

The Oura Ring 4 powered through just over 7 days in my testing, and the Samsung Galaxy Ring lasted 6. Nevertheless, the Circular Ring 2 outlasts most screen-equipped fitness trackers. The Fitbit Charge 6 lasted for 3 days in our rundown test, and most smartwatches need to be recharged daily.

Setup: Easy Start, Heavy on Personal Questions

To get started with the Ring 2, you need to download the Circular app and either create an account or log in. Then put the ring in the charging case, plug it in (the box includes a cord, but you’ll need to provide your own brick), and then press a button on the back of the case to wake it up and start charging.

(Credit: Andrew Gebhart)

An LED on the front of the case will blink to show the charging status: a green pulse indicates it's charging, and a solid green light means the ring is topped off and ready to wear. With the ring awake and charging, add a device in the app.

During setup, the app asks a series of questions to calibrate the data it collects and provide lifestyle recommendations. The questions go beyond typical demographic data and include interesting ones like “what time of day would I choose if I had to take a mentally taxing two-hour test?” It also asked what time I’d get up if I were free to plan my day, and what hours are best for me to learn something new.

After the questionnaire, the device asks for permission to find nearby devices, then it instructs you to remove the ring from the charger so it can send through any updates. Finally, it asks for permission to share data to train its algorithm.

(Credit: Andrew Gebhart)

Once the ring finished updating, I returned it to the charger until it reached 100% before I started wearing it. Like most trackers, the Circular Ring 2 can show some live measurements right away, but it needs a few days to collect enough info to populate most of the app.

App Experience: Dense, Complex, and Occasionally Frustrating

As noted above, the Circular Ring 2 collects a lot of data, and the app offers several ways to view your metrics and customize what it shows. The top of the page shows circles with scores for different metrics, such as energy and sleep. The higher your scores, the more colorful these appear, and you can tap them to view in-depth data for the category. Other circles offer quick access to features like guided breathing. You can also manage which circles show up on this page with a list of options via the farthest right circle.

Below the circles are more customizable shortcuts that default to features like a timer and a calendar. You can add options here, such as sports tracking, via the menu icon in the upper-left corner. Scroll down on the page for data charts, or hit the plus icon above the charts to switch to an AI assessment.

(Credit: Circular/PCMag)

Most data can be accessed either by clicking on the appropriate circle or scrolling down the page to find the associated chart. Once you tap a data set, you can easily switch to different metrics by tapping the icons beneath the chart. Because there's so much data, it often took me a minute to find specific numbers.

Even accessing basic features like exercise tracking can be unintuitive. Circular calls this Sports Sessions, and it's not in the default set of circles or quick access menu. You’ll need to tinker with settings a bit to make sure you can readily find the features you need. Once you’ve customized the app, it’s easy to scroll through what’s there.

The app can be slow to respond, especially when syncing your ring for the first time in a couple of days. Even at its fastest, the Circular Ring 2 would take roughly 90 seconds to sync during my first check-in of the day, but it often took minutes longer. Moreover, the app's server went down at one point during my testing, and I couldn’t access my data. On another occasion, the app repeatedly crashed while syncing my data.

A company rep acknowledged in an email that Circular experienced sync delays and server issues shortly after the launch of Ring 2, though an update in February supposedly brought increased stability. I tested it several months after that update, so the company still has some work to do on reliability.

(Credit: Circular/PCMag)

The Circular app also sent me a lot of notifications during my testing period. Like almost everything else in the app, notifications are customizable. In the settings menu, you can enable notifications for ideal bedtime alerts and best times to eat, drink caffeine, workout, and be productive. All of these are turned on by default, thus my notifications bar was flooded by Circular at first.

Even after trimming the list, it would occasionally send duplicate notifications, and sometimes a glitch would cause a single notification to be sent multiple times. Because the ring syncs slowly, I would occasionally get a notification with odd timing that had clearly been delayed, such as telling me it was a good time to be productive at a late hour when I was already getting ready for bed.

The notifications regarding activity timing mostly involve calculations based on that initial questionnaire. They didn’t seem to change much based on my energy and activity on a given day, so despite the frequency of Circular’s notifications, I rarely received one that I found useful.

Assessing the Data: Mixed Reliability Across Key Metrics

Taking an ECG with the Ring 2 is quick and easy. You have to stay still for the roughly minute-long process with your hand near your heart. The ECG result was anecdotally accurate in my testing. The Ring 2's stress level and energy assessments also seemed correct based on how I was feeling.

To further gauge the accuracy of its data, I intermittently wore the Ring 2 alongside the Apple Watch Ultra 3. I also compared metrics from the Ring 2 with those of the Moto Watch, which I’m testing for a future review.

Overnight, the Ring 2 captures stats like disturbances, efficiency, and tranquility. These numbers matched my experience and showed values that roughly aligned with the other devices. Its sleep cycle data also generally matched that of the other devices.

However, Circular occasionally showed gaps in sleep data. One time, it didn’t start capturing sleep until roughly 5 a.m., even though I had already been snoozing for hours. Another time, Circular thought I woke up slightly before 6 a.m., but I really slept until 7:30 a.m. that day.

(Credit: Circular/PCMag)

The Circular Ring 2 fared even worse when trying to capture exercise data. Smart rings fall short of wrist-based options for workout tracking, but recent models like the Oura Ring 4 have made strides in the right direction, offering limited but accurate data. The Circular Ring 2 isn’t accurate for workout tracking at all.

During a 30-minute run, it showed heart rate spikes and dips with no correlation to my actual activity and readings well outside the range reported by the Ultra 3. These numbers varied from the Ultra 3's by as much as 50 to 60 beats per minute (bpm), making it look like I was sprinting at max effort when I was simply maintaining a relaxed pace.

I sprinted at intervals at the end of my run, and the Circular Ring somewhat matched the Ultra 3’s heart rate numbers during those fluctuations, but the resulting chart after my run was all over the place. During a CrossFit workout, Circular's heart rate graph didn’t reflect the varied intensities of my routine, and it stopped showing a live value partway through my session.

The Circular Ring 2 doesn’t offer any kind of automatic workout tracking, whereas both the Oura Ring 4 and the Samsung Galaxy Ring do for certain workouts. Elevated activity and heart rate are accounted for in the rest of the data charts, but I couldn’t find any recorded sessions for my workouts outside the ones I manually started.

Overall, the Circular Ring 2 is almost passable as a sleep tracker, but it needs an update to address occasional data drops. It's poor at tracking exercise and needs a lot of improvements to be a good option on this front.