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I’ve reviewed smart rings for years. This is the worst one I’ve ever used

A person wearing the Circular Ring Slim.
Circular Ring Slim
MSRP $297.00
“The Circular Ring Slim is lightweight and comfortable to wear. Unfortunately, that's largely where the positives end.”
  • Comfortable to wear
  • App contains plenty of data
  • General advice can be informative
  • Aluminum isn't durable enough
  • Charger is inconvenient
  • No fitness tracking
  • Unreliable features, data, and app
  • Subscription or extra fees coming in the future
  • No third-party app integration

We’re at that stage where smart rings are becoming more popular. That means there are more choices, and we must be more vigilant before buying one.

A great example of why we need to pay more attention is the Circular Ring Slim, which may look attractive but is flawed in ways that make it unappealing. It’s certainly not all bad, but if you’re in the market for a smart ring, there are plenty of others you should consider first. Let me explain.

Circular Ring Slim: design

The Circular Ring Slim resting on a tree branch.
Andy Boxall / Digital Trends

The Circular Ring Slim lives up to its name, as the slender shape makes it easily the most comfortable smart ring I’ve worn. It’s a combination of the lightness and the slim case, which means I feel it less between my fingers and am sometimes not even aware it’s there at all. On several occasions, I’ve felt it with my thumb to make sure I’m wearing it after a sudden feeling I’d forgotten to put it back on after charging. It is about a millimeter wider than the Oura Ring, but I have not noticed any real difference on my finger.

The outside is entirely circular, while the inner part has a flat section where two metal plates for charging sit (next to the heart rate sensor set slightly to the side). It’s unassuming and ordinary, unlike the far more stylish Oura Ring, and only seems to come in a single matte black finish. The Circular Ring Slim doesn’t take inspiration from jewelry like the Oura Ring and follows the same design path as the Ultrahuman Air, appearing more like a functional product than something you’d choose to wear to complement your look or to make a fashion statement.

The Circular Ring Slim's sensors.
Andy Boxall / Digital Trends

I may not think the design is very inspiring, but others may like the mostly incognito look. There is one unusual design choice, and that’s the decision to put the Circular Ring Slim’s logo on the top of the ring.

It’s not hideous, but it doesn’t really add much to the overall look, and some may feel it cheapens it. I do think the company could have easily designed something a little more stylish to use in its place. It does supposedly serve a purpose, though. The Circular Ring Slim has a vibrating alarm, and you’re supposed to tap the logo twice to stop it vibrating. I say ‘supposed to,’ as despite setting the alarm multiple times, it has never vibrated to wake me up once.

I had high hopes when I first put the Circular Ring Slim on. If the functionality could match the outstanding comfort, it could easily become an Oura Ring competitor. Unfortunately, this would turn out to be one of the very few upsides to the Circular Ring Slim.

Circular Ring Slim: durability and reliability

The Circular Ring Slim, sitting on a lamp.
Andy Boxall / Digital Trends

Unlike the Oura Ring and the Ultrahuman Ring Air, the Circular Ring Slim is not made of titanium. It’s made of aluminum, and it really shows. I’ve worn the Ring Slim for just a few weeks, and it has already picked up chips and scratches on the underside, revealing the metal beneath the matte black finish. I have not done anything I haven’t done wearing the Oura or other titanium rings, which have not been marked in the same way over a much longer period of time. The smart ring has an IPX8 water resistance rating, but this also means it has no measured dust resistance.

The syncing process between the ring and your phone takes time, as the app imports data from the ring, syncs with the cloud, and then returns the data to the app. At this point, it mostly shows your stats, but at times, it can take a few moments before it all appears. The servers had a multi-day issue during my testing period, resulting in even slower times. The app and smart ring have received various software and firmware updates during my time using it, and these may have cured some of the problems I have encountered, but as they are intermittent, it’s hard to assess.

A person wearing the Circular Ring Slim, showing the underside.
Andy Boxall / Digital Trends

I’ve also encountered a problem where the app suddenly forgot the smart ring entirely, which prompted me to go through a convoluted reset process. This process involved putting the ring on the charger, taking it off ten times in a row, and waiting for a non-specific vibration to alert me that it had been reset.

I did this many times, usually unsure if the vibration alert was the one I should be looking out for, as it vibrates when you put it on charge anyway, but the ring refused to reconnect. Eventually, the problem seemed to cure itself, but it left me wondering if (or when) it would happen again. Poor user experiences like this make the Circular Ring Slim feel unfinished.

Circular Ring Slim: sleep and activity tracking

the Circular Ring Slim's app.

The reason you will want to wear a smart ring is to gain more insight into your health and wellness. The Circular Ring Slim only tracks your sleep and basic activity during the day; it does not track exercise or workouts, and there’s no way to add such activities into the app manually. It needs to make up for this by being a sleep-tracking superstar, but sadly, it’s not. It tracks sleep, but it’s not always very good at it, which then throws off all the other data it collects and the recommendations it makes.

Here’s an example. More than once, it has noticed when I’ve sat down in the early evening, and then it promptly decided I’ve fallen asleep. It then sees every subsequent movement before I actually go to bed as me waking up. By the morning, it thinks I’ve had hours more sleep than I’ve actually had, and with multiple awakenings. It skews all the data from this point, rendering anything it recommends entirely wrong. It doesn’t happen all the time, and the Circular Ring Slim does usually get it right, but it lowers trust.

 the Circular Ring Slim's app.

This also happened after the incredibly long 14-day calibration period, so I can’t pass it off as the ring just getting to know me. During this run-in time, the app asks a lot of questions, some of which are confusingly worded and hard to answer. However, the overall accuracy of the data did improve after those two weeks, so you should stick to it. Once that period had passed, the Circular Ring Slim’s “AI assistant,” Kira, comes along to provide daily recommendations and assess current performance and where you can improve.

Its advice is fairly generic stuff, and it can sometimes feel at odds with your body, too. I woke up to find a notification on my phone from the Circular Ring telling me that it was the perfect time for me to get some sunlight, which it sent about 5:30 a.m., and that didn’t seem very helpful at all. This aside, Kira does concisely present how your day compares to the previous few, which can help you understand where you can improve, and it does use percentages effectively to illustrate where you should try and make changes.

Screenshots taken from the Circular Ring Slim's app.

In addition to tracking sleep and basic activity, the Circular Ring Slim monitors stress levels and presents all the usual data points — including steps, heart rate variability (HRV), resting heart rate, blood oxygen levels, skin temperature, and breathing rate. Graphs include information on activity intensity and calories burned. The app has a button to check all these stats in real time, too.

Unfortunately, the Circular Ring Slim’s app does not have any third-party app integration, so if you exercise with Strava or a similar app, it won’t import or share data. It doesn’t connect with Apple Health or Google Fit, so its data can’t be used to better inform those platforms. The Circular Ring Slim is restricted to sleep tracking, isn’t always the best at this, and disappointingly closes itself off from the rest of the health and fitness world.

Circular Ring Slim: is the data helpful?

The Circular Ring Slim with the Circular app on an iPhone 15 Pro Max.
Andy Boxall / Digital Trends

The Circular Ring Slim provides three main scores for your day: Sleep Analysis, Energy Analysis, and Alarm Clock. The Alarm Clock is an odd one, as it’s mostly a screen to set your daily alarm, but it also shows if you woke up during the ideal sleep stage. The Sleep Analysis tab gives an overall sleep score, uses line graphs to present its data, and has a hard-to-interpret Sleep Duration chart.

Under the Energy Analysis page, daily movement is broken down into different sections, including a score for VO2 Max, plus line graphs on recovery, balance, and any variations in temperature and sleep quality. There are some historical graphs, but they’re hidden away and not all data gets treated and shown in the same way, so it’s quite hard to see exactly how your body has changed over time. You’d think the tab marked Calendar would show you a helicopter view of your stats, but it doesn’t and only shows a day-by-day.

I’ve never felt like I really knew what was going on with my body and sleep through the Circular app.

The app’s main screen shows what zone your body is supposedly in, such as a Productivity zone, and when it’s a good time to drink coffee, eat, or wind down for sleep. You have to check the app to see this information, though, as despite having all the notifications switched on, I have not received any on my phone regarding my zones. The Ring Slim has been connected to an Apple iPhone 15 Pro Max, and the app is also available for Android phones.

The app also shows a Cardio Points metric, but it doesn’t really explain how this is created, what it means, and how you can manipulate it. You’re also rewarded with “coins” for meeting various targets, and it cryptically teases you about how these may become useful in the future.

Circular also makes noise about its platform being free, but this won’t be true forever.  Explore the app’s menus, and you’ll find that important features like stress level monitoring, medication reminders, and alerts when your key stats suddenly change are “only free for a limited time.” You should know there is a subscription package incoming for the Circular Ring Slim.

A person wearing the Circular Ring Slim.
Andy Boxall / Digital Trends

The Circular app shows data, but unlike the Oura Ring’s app, it’s not very friendly to view, with its main scores placed in a section easily mistaken for a basic menu, and it doesn’t do a good job of really highlighting its scores.

I’ve never felt like I really knew what was going on with my body and sleep through the Circular app, and outside of Kira’s daily recommendations, there’s not much motivation or advice. It’s disappointing the app doesn’t highlight the core figures based on your data much, resulting in an app that feels a little thrown together rather than specifically designed.

Circular Ring Slim: battery and charging

The Circular Ring Slim on its charger.
Andy Boxall / Digital Trends

Circular claims the Ring Slim’s battery will last up to five days. During my time with the smart ring, it has lasted between two and four days on a single charge. This is several days less than the Oura Ring and the RingConn Smart Ring. There are two modes for the Ring Slim, Performance and Eco, and I’ve been using it only in the Performance mode. Why? Because Eco mode hobbles the heart rate sensor, doesn’t record sleep stages, and minimizes other data collection. If I’m going to wear a health and activity tracker, I want it to track my health and activity. I’m sure Eco would prolong battery life, but it’s pointless if it’s not doing much tracking.

The charger is one of the worst I’ve used. It’s about the same size as a USB thumb drive and has a USB C plug at one end and a pair of magnetic contacts at the other. The ring is attached to these contacts to charge. It takes some wobbling about to seat the ring properly, and it’s not all that secure once it’s in place. But worse than that is the whole inconvenience of the thing.

A person wearing the Circular Ring Slim.
Andy Boxall / Digital Trends

Because it doesn’t connect to a USB cable, it has to connect directly to a power adaptor plugged into a wall socket, and rarely are these set in a very convenient spot. Other smart rings use a charging puck linked to a cable, so it can be placed on your bedside table, ready to hold and charge the ring while you shower in the morning. You’ll have to fumble about next to the plug on the wall to do this with the Circular Ring Slim. It seems to take about an hour to recharge, and although I have seen one or two notifications telling me the ring is fully charged, most of the time, it doesn’t bother letting me know.

Circular Ring Slim: price and availability

A person wearing the Circular Ring Slim.
Andy Boxall / Digital Trends

The Circular Ring Slim is available for $297 through the company’s online store. The Circular website says sizing kits will be sent in March, while the Ring will ship in April. Circular also notes a “limited quantity” available, whatever that means.

The Oura Ring starts at $299 and requires a subscription of $6/month to use, while the RingConn Smart Ring is $279 and the Ultrahuman Ring Air is $349, and are both subscription-free. All three are better buys, but the Oura Ring remains the best. Alternatively, the Apple Watch Series 9 and Samsung Galaxy Watch 6 Classic are great smartwatches, which do a lot more than the Circular Ring Slim, and more reliably.

Let’s address the subscription situation. The Circular Ring Slim does not have a subscription at the moment, but one is going to come in the future. Not knowing how much a product will cost to own long-term isn’t favorable, so Digital Trends requested more details from Circular. Circular told us no decisions had been made on the eventual costs involved in using certain features or the timeline. It added that the mysterious Circular Coins currently collected may be able to be redeemed for some of the services on a daily basis, but again, no decisions have been made.

It’s simply impossible to recommend a product when we know some features will cost extra in the future, but not how much or when, or which other features it may suddenly decide to charge for.

Circular Ring Slim: verdict

The Circular Ring Slim and the Oura Ring.
Circular Ring Slim (left) and Oura Ring Andy Boxall / Digital Trends

Rather optimistically, the Circular Ring Slim’s information page says it was “Forged in Mordor,” a reference to J.R.R. Tolkien’s Lord of the Rings series. Well, you absolutely should not go on an epic journey to get the Circular Ring Slim, and it’s highly unlikely to become anyone’s “precious” if one is obtained, either.

From the concerning durability and the poor charging system, to the disappointing battery life and questionable accuracy and reliability, the entire package lacks polish. Indicating certain features will cost money in the future, but not saying how much or when, is unfair to consumers. Circular as a company started life on crowdfunding platforms, and although the Ring Slim wasn’t launched this way, it definitely has the same air to it. The concept is strong, but the execution isn’t.

The Circular Ring Slim shouldn’t be on your shopping list.

My weeks testing the Circular Ring Slim have been tumultuous. It hasn’t been the silent, reliable partner I expect a modern, fairly expensive health tracker to be, and having to put in so much effort so early on doesn’t bode well for me wanting to continue using it in the long term. This is a huge problem for a wearable device. My woes are not unusual either if the subreddit on Circular’s products is anything to go by. If my overall score seems harsh, it reflects how many aspects of the Circular Ring Slim need improvement before it becomes one to think about buying.

Smart rings are still in their infancy, and as more models make their way out into the world, you need to be careful about which one to buy. Right now, the Circular Ring Slim shouldn’t be on your shopping list. The Oura Ring remains the best smart ring you can get, or you can choose between any of the top smartwatches and get a far better product and service you’ll want to carry on using for years.

Editors' Recommendations

Andy Boxall
Senior Mobile Writer
Andy is a Senior Writer at Digital Trends, where he concentrates on mobile technology, a subject he has written about for…
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