Circular Ring Slim

I was invited to try out Circular’s Ring Slim. I have been wearing it for a few weeks and, well, let’s just say that I am yet to be convinced about the merits of it. But I have not tried a smart ring before so it could be that I have a more general issue with rings.

Circular is a French company and a relative newcomer to the health-oriented smart ring market – although its Pro model has been available for a couple of years.

The market sector that has been led by Finnish company Oura for many years. The market has not been particularly dynamic, although several players have emerged in addition to Circular including Ultrahuman, Amazfit and a few others. However, there are a number of big name players imminently entering the market including Samsung with its Galaxy Ring and, potentially, HONOR.

The Circular Ring Slim is Circular’s entry level product – with prices starting at €204 rising to €294 for Ring with a vibration engine. There’s no subscription, unlike with Oura.

By comparison, the just-launched Samsung Galaxy Ring is a significantly more costly £399/$399/€449.

Rings are a good way to track body metrics discretely. Many people don’t like wearing watches while sleeping, so a ring should be able to unobtrusively track a variety of biomarkers during both sleep and while awake. The downsides are that they are small, need partner devices to show the metrics, and battery life is modest.

The purchase process is also not straightforward as sizing is critical and difficult to manage in a predominantly on-line world. Most companies will initially send a fitting kit from which you can select the optimal size before ordering the actual ring. This adds friction and time to the purchase process. Companies with strong retail franchises, such as Samsung, maybe able to enhance the retail proposition to their advantage.

So let’s get into my experience with the Circular Ring Slim.

Fit and finish

The ring is light, weighing less than two grams and is just 2.2mm thick. The outer is made of a composite of titanium and carbon fibre. It feels quite solid but it looks like it’s made of plastic. Interestingly, the rings in the fitting kit I was sent are made of black plastic and these plastic dummies look remarkably similar to the actual ring. The inside of the ring is made from a hypoallergenic epoxy material. It’s clear in places, so it’s possible to see some of the components. The ring has a slightly thicker section which has two raised charging rails or bumps. These are unobtrusive when the ring is being worn, but help to stop the ring from rotating on your finger; the ideal position is with the thicker sensor part on the palmer side. The ring does tend to make my finger quite sweaty. I don’t think there’s any intrinsic heat coming from the device; it’s more a factor the materials used. My titanium wedding ring does not make my finger sweat.

The ring has held up well physically in its initial wearing. It’s IP67 rated, so swimming with it is no issue. While participating in a mountain race recently, I could hear the ring scraping on rocks while I was scrambling up rock faces. I was expecting the ring to have been damaged, but aside from some very minor scratches, it came through unscathed.

I selected a size 8 after using the sizing kit. The size 8 sits snuggly on my left pinkie finger. The fitting kit stated the ring can be worn on any finger other than the thumb. However, when the ring arrived, it contained information that the index finger, middle finger and ring finger are superior to the pinkie. Circular should add this information to the fitting kit.

Despite its diminutive weight, the ring contains a vibration engine – the only ring to have this feature so far. It’s not a strong vibe, but it can be used as an alarm, or as a reminder. It can also act as a prompt in guided breathing exercises that are included in the app. The ring has an unobtrusive logo on the top that can be tapped to, for example, stop the ring from vibrating during a wake-up alarm.

Vague charging time, unclear battery life

Considering that the battery is tiny, it seems to take several hours to fully charge. Circular claim it should fully charge in 45 minutes, which is about the same time as my Garmin Epix Gen 2 watch. It could be that the LED on the USB Type-C charging cradle flashes in a vague manner that doesn’t instil a lot of confidence in the charging process. After about three hours, the flashing stops, which should indicate a full charge. But even after fully charging, the charge indicator light sometimes starts to flash again – suggesting charging has resumed. The app does indicate the level of charge, but some firmer indications from the charging cradle itself would be welcome. Samsung’s Galaxy Ring charging case looks much more sophisticated, but then the Samsung Ring is over €100 more costly.

Ring in use, also vague

After taking the ring into use, it starts to build a set of data about the wearer. It does this in ‘performance’ mode, which is most energy intensive. Circular claims a battery life of 1.5 to 2 days in performance mode, while eco mode supports for up to 6 days of battery life. But in my experience it seems to last a little longer – up to 3 days in performance mode. Eco mode is of questionable value as it records metrics like heart rate infrequently and does not record sleep stages at all.

App tries hard

Rings, by their nature, don’t give much away about what they’re doing. There’s no display and the LED lights that provide for monitoring of biometrics, don’t illuminate unless the ring is on your finger – and then not full time. So you’re reliant for most interactions on the smartphone app. Fortunately, the Circular app itself is fairly good. However, while it integrates with Apple’s Healthkit, it doesn’t appear to integrate with other health frameworks – for example Google Fit or Garmin Connect. This means that it can miss incorporating information from other sources that could enhance its knowledge of a user’s general health and activity levels.

My main issue though is that it seems to miss data if the ring is not synchronised with the app at least daily. Circular claims the ring can store up to 10 days of usage data for later synchronisation, but this is not my experience.

Sports activity

You can record sports sessions on the ring – the app has more than 50 activities to choose from (although the names of some are spelt incorrectly). The ring does not have any GPS capability and is therefore reliant on a partner device such as a smartphone for actually tracking distance. The ring itself uses its motion sensing and heart-rate monitoring. It ups the frequency of heart-rate monitoring during sports sessions to full time, unlike at other times when it monitors part of the time.

I was interested to see what it made of an ultra-marathon I did. I charged the ring before the race, however I didn’t inform it via the app that I was undertaking a sports activity. To do this, the app needs to have a data connection. If the connection is poor, it can take a long time to initiate a sports activity session or doesn’t manage it at all. For the race, I was in an area with no cellular and no WiFi coverage – so there was no way of starting the sporting activity on the ring. Nevertheless, given Circular’s claims that the ring can store up to 10 days of usage data I was expecting it would at least track the number of steps I took. But after syncing the ring, it shows no data at all for the period from the Wednesday through to Tuesday – the race was on the Saturday. There is no explanation of why the data is missing despite me wearing the ring all the time it wasn’t charging.

The ring only seems to sync with the app when you ask it to, it doesn’t sync in the background. However it does try to sync whenever the app is opened. This is also perplexing as the syncing process is slow. If I am interpreting the little sync icons correctly, the sync process involves moving data from the ring to the phone, and then up to the cloud, back to the phone and then, presumably, some processing occurs within the app on the phone to generate the usage data that is displayed. The sync portion typically takes just over a minute, and then the on-device processing takes another minute or so. Two minutes doesn’t sound long, but if you sit and look at the little icons whirring away, it can seem an age and, in most cases, I can’t be bothered to wait and have moved on to other things.

Wellness Score

Once syncing is complete however, the app provides some useful feedback on the metrics and suggestions for how to improve any that are below par. Circular uses an AI algorithm called Kira+ to make the recommendations. The main metric is a ‘Wellness Score’ that takes into account things like sleep and energy analysis. However, while the app has nice little animated circles for the component parts, there is no circle for the overall Wellness Score, which seems odd.

And in the individual component scores, the scoring system seems a little strange. My sleep score on the day this was written (not when the above screenshot was taken) was 84, which seems like it might be quite good. But it’s actually rated ‘Inadequate’ by the app, although inadequate actually equates to how I feel; I slept quite badly and then got up very early to go cycling with some buddies. As a consequence, I have felt a little jaded all day. But my energy score is given as 94 and graded as ‘Optimal’, which is not how I feel.

The recommendations provided by Kira+ mostly seem reasonable, but one has to trust that the metrics have been faithfully captured and that the science underlying the recommendations is correct. I find myself doubting this because when I compare metrics gathered across two smartwatches and the ring, the ring is often significantly different.

Heart Rate

Sitting at my desk right now, the ring says my heart rate is 120 beats per minute, while my Garmin and Apple Watch are both agreeing on around 57bpm. Using a finger to measure my heart rate manually confirms the watches are accurate. This means the ring is massively inaccurate. Measuring pulse at rest is the easiest task. How about while moving?

Last Saturday, I ran 15km. To measure the workout I used three devices. Firstly, my Garmin Epix Gen 2 watch together with a Garmin heart rate strap. This is the most accurate heart rate monitoring method available to me. I also used the Apple Watch Ultra with wrist-based heart rate monitoring. And the Circular Ring Slim.

The Apple Watch Ultra is not a great athletic monitoring device as the touch screen remains active during workouts (apart from swimming). On this occasion the Apple Watch managed to accidentally end the run, start several other different types of workout and generally misbehave. However, it is good at wrist-based heart-rate monitoring and for the period it was recording my run, it was identical to, or just a few beats different, than my Garmin Epix and heart rate strap.

It is harder to interpret the data from the ring because it doesn’t segment the run in the same way. While the average recorded heart-rate – a suspiciously precise 126.6 bpm – is not very dissimilar from the Garmin’s 131 bpm, the ring recorded a high of 166 bpm, while the Garmin recorded a maximum of just 153 bpm. And looking at the graphs provided by the two devices, it’s easy to see that the ring produced more wild spikes than the Garmin. The run was steady with a few hills, but I wasn’t doing sprints or anything of that nature that would cause wild fluctuations in heart rate. I can only conclude therefore that the ring didn’t do a great job, and the superficially similar averages is more a coincidence than through any specific accuracy on the part of the device.

The same activity shown on the Garmin Connect app versus the Circular app

Sleep

Recording sleep is one of the principal benefits promised by smart rings. Some people don’t like to wear watches while they sleep finding them uncomfortable, whereas a ring can be worn with little impact on comfort.

The problem with any comparison is that recording sleep is notoriously difficult to do for a consumer wearable device. The only reliable way to monitor sleep is to apply multiple sets of electrodes on the scalp that can measure brain activity. Any other device is reliant on interpreting some combination of motion, heart rate, and, in the case of the Circular Ring, skin temperature.

I almost always wear my Garmin watch when I sleep and I have come to have reasonable confidence in what it reports. For example, last night, the Garmin correctly detected that I woke relatively early, went to the bathroom but then got back in to bed for a short snooze. I was interested to see if the Circular ring correctly detected the same, but because I had switched the ring to Eco mode, I discovered that it doesn’t record sleep stages and is only able to determine approximately when I went to bed and when I got up – nothing more nuanced than that.

Looking at prior nights, when the ring was in performance mode, and comparing with my Garmin, I find little consistency between what they report. I have not provided comparative, side-by-side data in this article, but from studying the sleep analysis provided by my Garmin and by the Circular ring, there is little more than superficial agreement between them. And at the detailed level, there is almost no agreement. I don’t know which, or if either, is correct, but I don’t have a huge amount faith in the sleep analysis provided by the ring.

Circular does say that its Sleep Staging Algorithm will improve over time to achieve 80% accuracy compared to polysomnography.

Steps – in the wrong direction?

Counting steps is among the most basic metrics for any activity tracker and they should be able to do this with decent accuracy. However, the Circular Ring Slim is often wildly optimistic. For example, checking the status for today, the ring reports that I have covered an impressive 10415 steps, while my Garmin watch reports a more conservative, and likely more accurate, 5120 steps. I have noticed this sort of inconsistency on other days that I have checked. I was really interested to see what the ring recorded during the ultramarathon – my Garmin recorded 85,000 steps. However, as previously mentioned, the ring recorded nothing at all.

Final Thoughts

I was interested to use a ring – it is one of the few wearables I had not experienced before. And with Samsung and potentially other players entering the market – rings are likely to get a lot more attention.

But after wearing the Circular Ring Slim for the last few weeks, I am left wondering if I would recommend it to anyone. A ring should be a good option for those who just want a device they can ‘fit and forget’, but, at least with Circular, it’s a device that needs to be carefully managed to get the best from it, and even then, I am left questioning the quality of the data captured, which means the interpretation is of less value than it might otherwise be. My colleague says that trust arrives on foot, but departs on horseback. I am still waiting for my trust in the Circular ring to arrive.

Consumer wearables are always going to be a compromise in some areas, but with the Circular Ring Slim, I feel that there is too much that is compromised to offer a strong value proposition.

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