A number of companies are looking beyond the wrist at the next frontier in wearable technology. Few people know that the finger can provide a useful snapshot of a person’s overall health. This is because it contains arteries that can be sensed by finger-worn devices to capture physiological data such as your heart rate and blood oxygen.

Slim and sleek, smart rings are generating lots of interest. Particularly amongst people who are after something that is useful, as well as lightweight and fashionable. The big brands, such as Apple, Fitbit, and Garmin, are yet to enter this area. But there are a few other players with interesting offerings.

One of these is Wellue. Their FDA-registered O2Ring continuously monitors your blood oxygen (SpO2), heart rate, and movement with clinical-grade accuracy. Slip it onto your thumb or index finger and it will do the rest. You can view data in real-time on the device itself, or sync the ring with the app or the accompanying PC/Mac software for detailed analysis and reports on trends.

Typically retailing for $169 on getwellue.com , the O2Ring is more expensive than a typical fingertip blood oxygen monitor. Is it worth the extra price? I set out over the past week to find out.

Wellue O2Ring review: Design & hardware

• Feels solidly built – rubberised design
• More about functionality than fashion
• Large, easy to read display
• 12-16 day battery life

Look & feel

Despite the name, the Wellue O2ring is not a ring in the classical sense. The device is made of soft silicone that has a rubberized feel to it. It is also larger than a typical ring so is more about function than style. But it is smaller and much less cumbersome than fingertip blood oxygen monitors which it is meant to replace.

The actual size of the device comes in at 4 x 3 x 3.5cm (L x W x H) and weight at 15 grams. It fits fingers that measure between 50 and 82mm. The rubberized band stretches so can expand for those with large fingers.

While it is not fancy, the whole thing does feel solidly built. A large screen sits on top which is easy to read thanks to its size.

On one side of the display is a touch key that you can use to wake up the screen and cycle through time, heart rate/oxygen level readings. There’s no power button. As soon as you slip on the ring it will turn on the sensor and the screen will spring to life. When you remove the ring, it will switch off automatically after a few seconds. I really liked this, as most of my other devices require powering on and off. The touch key is also very responsive.

You are meant to wear the O2Ring on your thumb finger. If that feels too tight, the other option is to use the index finger. I found the band approach to be much more comfortable than fingertip alternatives as it does not get in the way of anything. You can type and do pretty much anything you want while wearing the ring.

To properly test it out, for a week I wore the Wellue O2Ring every night during sleep. With all the typical tossing and turning it stayed in place and never felt in danger of slipping off. The rounded corners on the device mean that it does not snag on the bed sheets or pillows. In fact, the ring is so comfortable, I would wake up in the morning forgetting it is even on.

The only part of the design I am a bit cautious about is the flexible tip at the end of the silicon band. It seems a bit flimsy. I am not sure if it might break at some point with long-term use.

Unlike some other smart rings, this device is primarily meant for use at home or in healthcare facilities. The bulkiness of O2Ring means it is something you would probably not want to wear in outdoor environments anyway. You could if you wanted to. But blood oxygen readings are best taken while at rest or sleep so there would be little point in taking measurements in those conditions.

Wellue says the device is designed to give medically accurate readings during sleep when you are sitting somewhere or walking slowly. Some of their customers are professional pilots. They use the O2Ring to monitor their blood oxygen when flying planes.

The device has an IP24 rating for dust and water resistance. So you should not take a shower or bath with it, but you’ll probably be ok to wear it in the rain.

Under the hood

The technology that is used by Wellue O2ring is something called transmissive oximetry. This is trusted and used in hospitals and clinics. Smartwatches use reflective technology which is not seen as accurate.

With transmissive oximetry, a device passes two wavelengths of light through a thin part of the body to a photodetector. It then measures the changing absorbance at each of the wavelengths. Fingertips are perfect for such measurements as they have higher blood flow rates than other tissues. Hence the accuracy of the O2Ring and traditional clip-on fingertip oximeters.

The O2ring has built-in memory which enables it to work independently without a phone. There are 4 small memory cards built-in. Each can store about 10 hours of data.

This means you do need to sync with the app from time to time. So if you track sleep each night, after four or five nights you’ll need to fire up the app. If you don’t, the oldest recording will be deleted when the memory is full. Async is done automatically when connected via Bluetooth 4.0 to the smartphone app or computer software.

Apart from accuracy, what distinguishes the O2Ring from other such devices is the sampling rate. Oxygen levels, pulse rate, and motion data are captured at 1-second intervals. For those with medical conditions such as sleep apnea, the high sampling rate will be very important.

Battery life

As far as the all-important battery life, the oxygen ring has an advertised running time of between 12 and 16 hours on a single charge. Wellue says this is enough for two nights. In practice, though, I found that it was best to charge it after a full night’s sleep. I tend to sleep at least 8 hours per night and it definitely wouldn’t last me a full two nights.

Charging is done via a micro-USB cord. Unfortunately, there is no progress bar or percent charged on the display, so you will need to leave it on until the display turns off. It can take more than an hour to go from zero to full so it is not that quick.

The battery inside the Wellue O2Ring is similar to a coin cell for watches. So theoretically, you could replace it yourself if needed, or ask a repairman to do it. But the battery should last a few years so there probably wouldn’t be any need for that.

Wellue O2Ring review: Functionality

• Clinical-grade data, FDA registered for accuracy
• Choice of smartphone app or PC/Mac software
• Abnormal SpO2 and heart rate alerts
• Export high-resolution oxymetry reports to share with doctor

Setup and first use

For me, a highlight of this product is that it is incredibly easy to set up and just as easy to use. Start off by downloading the ViHealth app to your iPhone or Android device. Open it and create an account.

Slip your finger in O2Ring (or plug it into the charger) to switch it on and the app will find it and ask if you want to pair. Click on the picture of the ring and you’re done. From that point on it will link up automatically whenever the ring is switched on and the app is open. You can also use the app in offline mode to review data when the ring is off.

At this point, you might want to tweak a few options. Go to the “Settings” tab in the app where you will have the option to connect with Apple Health and where you’ll be able to turn on the heart rate and oxygenation alarms. This will also allow you to set up the high and low thresholds for each.

The O2Ring vibrates to alert the wearer if he or she has approached the preset limits. The idea is that this will warn you of heart abnormalities or hypoxic events so that you can take a break to recover. So, for example, if your oxygen level dips below the configured threshold during sleep, the vibration will wake you up so that you can adjust your sleep position.

For those that suffer from sleep apnea, this is a feature that cheap oxygen monitors simply do not have. So this feature alone justifies the higher price point of the Wellue O2Ring as compared to such devices. 

The discreet vibration also helps your partner sleep better. Think of it as a vibrating smartphone. Something like this is great for meetings and noisy environments. Mind you, there’s no built-in speaker in the ring. However, the mobile app can sound audio alarms if that is your preference. You can even use both at the same time, the vibration alarm on the ring and the sound alarm on the phone.

I do feel, though, there is a missed opportunity that could be fixed with a firmware update. Considering the vibration functionality is already there along with a clock, it would be nice if the O2Ring could act as a morning wake-up alarm.

Lots of informative data in the smartphone app

You can use the ring itself for real-time blood oxygen and heart rate readings. Once you slip the device on it will automatically start to capture the measurements for a minute or so before shutting off the display so you can sleep. Dead simple. The real-time data can also be seen in the dashboard of the app.

I found the Perfusion Index (PI) to be a nice feature. Similar to an indication of the strength of a cell phone signal, it quantifies the quality of the pulse reading. This can vary depending on lots of factors such as the way you wear the ring, physiological conditions, skin temperature, and more. You can use it to assess whether you are wearing the device correctly. As long as PI is green you are good to go.

In the morning, you take off the ring, and the display will briefly turn on and start a count-down from 10 to 0 and then a “SAVING” and “END” message. After that, you can turn on your phone, open the app and allow it to sync.

Blood oxygen measurements appear to be accurate when compared with a traditional oximeter. That’s to be expected considering Wellue has secured FDA approval for the device. Plus measurements are captured each second and displayed in four-second intervals in the app. Much more useful than Apple Health which only shows SpO2 data in 10-minute intervals.

The “History” tab in the app shows you a timeline of all your measurements. What I didn’t like is that each time you remove the ring, it saves the session as a separate one. So if you take the ring off in the middle of the night and put it back on, two data sets will be created. So in that sense, it can get a bit messy.

Each individual session shows a wealth of data. There is a handy O2 score bar that quantifies your oxygen shortage during sleep. It combines frequency, duration, and depth of oxygen drops. In my case, I was typically at 9.8 and 9.9 which is considered to be excellent. If the Score turns yellow or red, Wellue suggests you speak to your doctor for advice. To make this easier, the O2Ring can create a SpO2 report in PDF format that you can email to your doctor.

Other data shows your average pulse rate for the session, average SpO2, the number of drops over 4%, lowest SpO2, and more. All very useful stuff that goes into more detail as far as blood oxygen than any other device I’ve come across. Nothing really out there allows you to create four-second interval, high-resolution oximetry reports that can be shared at the click of a button.

There’s also a PC, MAC app that you can optionally use

I also liked the fact that you have the option of installing PC or Mac software called O2 Insight Pro. Simply download it from the Wellue website.

It works exactly the same way as the smartphone app but everything is displayed on the large screen format that is easier to read. You’ll have no trouble detecting in detail the hourly graphs – it is comparable to an actual sleep study report.

Wellue O2Ring review: The bottom line, is it worth it?

The Wellue O2Ring is a very useful product. But it is not for everyone. The device is primarily designed for people who need to track their oxygen levels in detail, especially those who have or suspect they have sleep apnea or another medical problem. If you’ve recently tested positive for Covid-19 this ring might give you peace of mind. 

The device predominantly does one thing and it does it well – it tracks your blood oxygen in one-second intervals with medical-grade accuracy. Other stats that you’ll get are heart rate and body movement. The thing will also buzz you into alertness if you are experiencing low oxygen levels or irregular heart rates. For those that suffer from sleep conditions, it could be a lifesaver. Shift your position and the buzzing will stop.

The ring is quite big in size so it is not something you would want to wear around the clock. But for measurements at home, in the office, or overnight it is quite useful. The device is also well made and comfortable to wear, in my case on my thumb.

Typically retailing for $169 on getwellue.com, the O2Ring is expensive if all you need are ad-hoc blood oxygen and heart rate readings. A typical fingertip pulse oximeter is a much cheaper option. But if you need overnight monitoring with alarms and long-term tracking then it is probably the best option out there. For some, it might become their most important piece of jewelry.