Prevention Circul+ smart ring review

A health tracking smart ring that delivers good data, but not a great design
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Prevention Circul+
By Prevention
The Prevention Circul+ feels like a medical device that's not quite ready for consumers. It's let down by poor design and terrible battery life, which makes it hard to want to keep on wearing the Circul+ on a long term basis. For key sleeping vitals it just does the job. As far as being the perfect health tracking smart ring, it's misses the mark.

  • Rich health tracking
  • Reliable and accurate insights
  • Easy set up
  • Awkward design
  • Charging setup isn't great
  • Short battery life

The Prevention Circul+ arrives just as the smart ring market is starting to hot up.

The space has been dominated by the Oura Ring 3, but the Circul+ and forthcoming Movano Smart Ring show there's a big future for the segment.

The Circul+ is a partnership with Bodimetrics, and offers ECG, blood pressure monitoring, temperature and tracking heart rate and blood oxygen levels 24/7.

In addition to that, it'll also track sleep including breaking down sleep stages, keep tabs on daily step counts with a free companion app to review all of your data.

At $299, it costs the same as a the latest generation Oura Ring but doesn't need an additional subscription.

We've been living with the Prevention Circul+ for a while now to see if this is a smart ring that's worth keeping on.

Prevention Circul+: Design and comfort

Prevention Circul+ smart ring review

Any wearable needs to be wearable – something that's easy and pleasant to wear. Sadly, that wasn't the case with the Circul+.

It's awkwardly designed, and doesn't look like a normal ring, so it doesn't disappear into the background – it's conspicuous, chunky and ugly.

It comes in a matte black look in small, large and extra large sizes, with ring sizes attached to those different models to make sure you get the ideal fit. There's no sizing kit involved in the process – unlike Oura – so you'll need to have an idea of your index finger ring size before making your selection.

We had the smallest size option, which still wasn't the sleekest of things – and putting it side-by-side with an Oura Ring (below), you can see just how different this ring is going to sit on your finger. it did fit, and didn't feel tight, but it wasn't the wearing experience we expected.

Prevention Circul+ smart ring review

Oura Ring 3 (left) and Circul+ (right)

The design is semicircular in look with a flatter part below that sits against the bottom of you finger where the sensors are placed. There's also a protruding edge to that flatter part to help better accommodate those sensors and when it needs charging.

To get the ring onto your finger, it uses a spring loaded mechanism on either side of the ring you can simply lift making it very easy to slip and off.

When it's on, you know it's on, Particularly at the bottom of the ring, which sits a little too snug for our liking and while it's a relatively light design, the weight that is there is noticeable. It wasn't the most comfortable to wear when typing away at keyboard and it's certainly one you couldn't really wear in the gym or for exercise either.

It felt more acceptable to wear it at night, especially as some of the more interesting metrics are capturing during sleep, but those design gripes don't entirely disappear either when it's time to nod off.

Prevention Circul+ smart ring review

Things don't get much better with charging setup for this ring. The cradle is built into what looks like a dinky microUSB stick clearly designed primarily to be charged up in a laptop. You'll need to drop your ring onto the top of the cradle and wait for the green charging light on the ring to illuminate to indicate you're doing it correctly. The connection though felt a bit too flimsy and it always took a few attempts to get the ring to sit and charge.

The ring has been given an IP65 dust and water resistance rating, which means you do get some extra durability protection here, but ultimately it's not something you can wear in the shower or go swimming with.

For a smart ring that's designed to be worn all day and night and to go about its tracking business in the background, the design isn't there to let you do that. We've been spoilt using smart rings like Motiv and more recently Oura, and the Circul+ doesn't quite live up to the same sleek, stylish design standards.

Prevention Circul+: Health monitoring features

Prevention Circul+ smart ring review

This ring is promising a level of health tracking we haven't yet seen on a smart ring and it's tracking that according to Bodimetrics, has been medically tested and is designed to work on all skin tones.

It features a 3-wavelength photo-electric sensor to deliver heart rate and blood oxygen tracking day and night. It can also track temperature during sleep, and there's support now included to take a single lead ECG measurement and track blood pressure.

Doing the latter requires calibrating with a blood pressure monitor first, so it's a similar setup to the blood pressure tracking support on Samsung's latest Galaxy Watches.

There is some talk of the level of accuracy to expect with some of those measurements with resting heart rate data accuracy stated to be plus or minus 2bpm against medical grade monitoring.

For SpO2 monitoring, it's +/- 3% accuracy in terms of readings. The pulse oximeter support is also validated to work on all skin tones. That's down to placing the sensors at the bottom of the ring, to improve how the ring can shine wavelengths of light through the skin to take measurements from those pulsating blood vessels.

So how well does the tracking fare? Well, we'd say good overall. All of the data is collected in the Circul+ app (Android and iOS) where you can see a dashboard with your stats, find reports on sleep and guides to better understand the included features.

Prevention Circul+ smart ring review

To view real-time heart rate and SpO2 readings, you'll need to launch the app and once the ring has decided to connect, will display those real-time readings.

If you want use it for continuous monitoring, you need to manually turn that on, picking from daily, sleep and exercise monitoring modes.

We compared real-time resting heart rate readings and SpO2 readings with a dedicated iHealth pulse oximeter and they pretty much matched up in all of the readings.

As promised, there was generally a difference at most of around 1-3bpm and around 1-3% for blood oxygen readings.

We also compared readings to the Oura Ring 3 and found they offered similar resting heart rate insights.

Prevention Circul+ smart ring review

ECG compared: Circul+ data (left) and Apple Watch Series 7 ECG (right)

If you want to take blood pressure readings or an ECG reading, you do have scope to do that here too.

For the blood pressure reading you'll need to input blood pressure readings from a cuff-style monitor first to calibrate the feature. Then you'll need to follow the instructions for the ideal scenario to take a reading before placing your finger on the electrode on the bottom of the ring.

After the reading is completed, your report will be generated displaying blood pressure and electrocardiogram readings.

We compared data to a blood pressure monitor and found the data was within the +/- 3% accuracy band.

The ECG goes way further than Apple Watch or consumer wearables, and the data produced is more in line with a medical device – rather than a quick examination of afib/sinus rythtm.

Prevention Circul+ smart ring review

Blood pressure compared: Circul+ data (left) and Kinetik blood pressure monitor (right)

There's no actionable insights here at all, it's really about presenting the data to you and letting you interpret or share and export the data to a medical professional if you wish.

The data on the whole felt good enough, but didn't always 100% match up for instance with another ECG device or blood pressure monitor.

It fared much better for SpO2 and real-time heart rate readings. The fact you have to manually turn into continuous tracking mode than can feel annoying though and there's elements of the process overall that felt clunky in places.

Prevention Circul+: Fitness and sleep tracking

Prevention Circul+ smart ring review

It isn't all about serious health monitoring with this ring though. You can use it as a fitness tracker and to track heart rate during exercise.

Unfortunately, the design and fit made it hard one to get on with when it came to using it for exercise or even simply counting steps.

A lot of the time we attempted to keep it on for exercise, it just felt like a nuisance to wear. If you were doing less energetic workouts, you'd might be able to forgive the fit, but it's something we really struggled with.

It fares a bit better for basic fitness tracking capturing daily step counts and estimating calorie burn. Step counts were in the ballpark of the Oura Ring 3 with data never feeling wildly out.

You're not going to get nudges to keep moving or be able to expand on data beyond simple step counts. The step counting doesn't appear to be saved in the app either, so you'll get to see what you've done for the day before it refreshes for the next day.

Where you're getting a little more insight is with sleep tracking, which is delivered in the same way as most other wrist-based sleep trackers do, via onboard accelerometer motion sensors detecting when you're asleep. You'll need to manually turn on the tracking in the app to get all of your sleep data though.

Prevention Circul+ smart ring review

In the morning, the app will display sleep duration, sleep stages including REM time, and will additionally capture heart rate, baseline skin temperature and SpO2 levels including an oxygen desaturation index.

An index score of less than 10 is normal, above 10 is mild and above 30 is severe. It's an important insight with relation to diseases like Hypoxemia or Chronic Obstructive Pulmonary Disease (COPD).

Prevention Circul+ smart ring review

Sleep tracking compared: Circul+ (left), Oura Ring 3 (centre) and Polar Pacer Pro (right)

Accuracy-wise, we compared it to the Oura Ring 3 and Polar's usually very reliable sleep tracking – and we found the data comparable with both of these devices, with no worrying anomalies.

Average sleep heart rate data largely matched up with the two devices, though at times lowest heart rate readings seemed strangely low.

Other data like temperature and SpO2 data felt reliable too, though much like the health monitoring outside of sleep, there's no insights on offer to help you better understand the data.

Prevention Circul+: Battery life

The Circul+ battery life is based on using its continuous monitoring support and that gives you 16 hours of time to track, which isn't very long at all.

The problem is that if you choose to continuously monitor during the day and then decide you want to track data during sleep, it's simply not going to stretch.

If you're not wearing the ring and it's powered up, the battery does drain the process. So there were plenty of time when we'd fully charged the ring, connected it to the app to check in on real-time readings, took it off and the battery drained entirely.

That meant when it often came to night time, the ring was already out of power or didn't have enough power to track through the night.

Coupled with the far from perfect charging setup, and the small battery and the way you have to charge the ring in spite of its pocket-friendly design, isn't the ideal combination.

How we test

Michael Sawh


Michael Sawh has been covering the wearable tech industry since the very first Fitbit landed back in 2011. Previously the resident wearable tech expert at Trusted Reviews, he also marshaled the features section of

He also regularly contributed to T3 magazine when they needed someone to talk about fitness trackers, running watches, headphones, tablets, and phones.

Michael writes for GQ, Wired, Coach Mag, Metro, MSN, BBC Focus, Stuff, TechRadar and has made several appearances on the BBC Travel Show to talk all things tech. 

Michael is a lover of all things sports and fitness-tech related, clocking up over 15 marathons and has put in serious hours in the pool all in the name of testing every fitness wearable going. Expect to see him with a minimum of two wearables at any given time.

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