Article updated on November 26, 2020 at 3:00 AM PST

Apple Watch Series 6: SpO2 tracking is still in its early stages

Apple's new smartwatch can detect blood oxygen levels throughout the day and night, but can't be used as a medical device yet. So what is it for?

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Vanessa Hand Orellana
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Vanessa Hand Orellana CNET Senior Editor
As head of wearables at CNET, Vanessa reviews and writes about the latest smartwatches and fitness trackers. She joined the team seven years ago as an on-camera reporter for CNET's Spanish-language site and then moved on to the English side to host and produce some of CNET's videos and YouTube series. When she's not testing out smartwatches or dropping phones, you can catch her on a hike or trail run with her family.
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The Apple Watch Series 6 feels like it has perfected many of the features I liked about its predecessor. It has a brighter always-on display, a more powerful processor, faster charging and two new colorful options to choose from. But the feature I was most excited to try out was its new sensor that measures oxygen saturation in the blood (aka SpO2) with the tap of a screen. As someone who panic-bought a pulse oximeter at the start of the coronavirus pandemic and still checks her levels at the first sign of a cough, the thought of having one strapped to my wrist at all times was enough to pique my interest.

But unlike the ECG feature on the Apple Watch, which has been tried, tested and cleared by the US Food and Drug Administration, along with the irregular heart rhythm notifications, SpO2 on the Apple Watch still seems to be in its early stages. Navigating all this new data can be daunting for anyone who's not a medical professional. 

SpO2 leaves some unanswered questions

I bought an FDA-cleared pulse oximeter, the device doctors use to measure SpO2 on your fingertip, as a precaution when coronavirus cases in the US started to climb. Having low blood oxygen levels doesn't guarantee you have COVID-19, but it's one of the major symptoms of the disease. I had read horror stories of people who waited too long to go to the hospital and had died in their sleep because they didn't realize their levels had dipped overnight. You should always check with a physician if you are experiencing shortness of breath (another symptom of COVID-19), even if a pulse oximeter says you're in a healthy range, but I found comfort in knowing that I could at least use it as a reference if I ever experienced shortness of breath. 

That's not something you can do with the Apple Watch -- Apple says it should be used for wellness purposes only and not as a medical device, meaning you'll have to take the results with a grain of salt and shouldn't use it to screen for any type of disease, which is what I had been hoping to get out of it. But there may be other advantages of having it strapped on your wrist at all times. 

Much like a pulse oximeter, the Series 6 uses red and infrared light from its new sensor to determine the percentage of oxygen in the blood. But instead of shining the light through your fingertip, it uses the light that's reflected back from the blood vessels in your wrist to determine your oxygen levels based on the color of your blood. 

Watch this: Apple's new Watch Series 6 with SpO2 tracking and cheaper Apple Watch SE

During the setup process you're asked whether or not you want to activate SpO2 tracking, which I did, but you can always go back and disable it in the settings after the fact. The first thing I did after strapping on the Watch was open the Blood Oxygen app. It gives you a few tips on how to get the best result and you need to rest your arm on a table or flat surface while the Watch is taking a reading. Then the 15-second countdown begins and you're done -- straightforward and painless. I got a 95% on my first read, which was lower than what I'm used to from my pulse oximeter. Anything above 90% is generally considered by clinicians to be within a healthy range, but in most cases, higher is better.

I tested it a few more times and got slightly different results within a few percentage points depending on whether I was completely still and silent during the test, where I had the watch positioned on my wrist and how tight the strap was. There are many factors that can affect a reading, such as skin temperature or the position of the sensors on the body. Side-by-side with my pulse oximeter, the Apple Watch was often off by about one or two points, but sometimes spot on.  

Apple Watch Series 6 Product Red from every angle

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Measuring blood oxygen levels over time

What was more interesting to me was the SpO2 data that collected over time in the Health app . That's something my pulse oximeter can't do. Unlike the Galaxy Watch 3 , which only does spot checks, the Apple Watch also takes background measurements throughout the day (and night). Click on the Respiratory option on the dashboard and you'll see all your measurements plotted on a graph which you can view a day, week or month at a time and filter by time of day or percentage. But it's up to you, or ideally your physician, to interpret this data. 

Vanessa Hand Orellana/CNET

I've been wearing the Apple Watch for six days and I generally fluctuate between 95% and 100%. My level is usually at the lower end of that range during the night as your breathing rate is reduced somewhat. But there were two nights or early mornings where my levels dropped to 92%, which scared me a bit. I was below what the Mayo Clinic considers a "healthy range," but above what's considered a "low range." Should I be concerned? Dips in oxygen saturation can signal anything from sleep related conditions like sleep apnea to asthma, or even respiratory viruses like COVID-19, but I don't know exactly how low and how often it has to happen for it to be a problem, and the Apple Watch can't answer that. I wish the watch could let me know if something was off, the way it does with the low, high or irregular heart rhythm alerts so I could finally put my little pulse oximeter to rest. Maybe in the future, and with enough data and medical studies, it will.

Apple currently has three different SpO2-related studies underway, including one related to asthma and another for detecting early signs of respiratory illnesses such as COVID-19.

With the Series 5 discontinued, the Series 6 is also the only watch you can get from Apple with the electrocardiogram feature, which Apple calls ECG, that debuted on the Series 4 in 2018.

New colors, brighter screen

Aside from the sensors on the back, the Apple Watch Series 6 could pass for a Series 5. They have the same body and similar always-on display. It wasn't until I put them side by side that I noticed a difference. While the screen on the Series 5 dims when not in use, the Series 6 almost looks like it's still on, which is especially helpful when you're outdoors. Apple says it's 2.5 times brighter and it shows.  

It's also the first Apple Watch to add to the traditional silver, space gray and gold finishes. Mine came in a Product Red aluminum frame. That aluminum version also comes in blue, while the stainless steel gets a new gold finish. 

I like the red, but I think I'd still stick to a more neutral tone for the frame and spice it up with a watch band instead. 

Claspless bands and Memoji watch faces 

Apple also announced a new type of silicone band with no clasps or buckles called the Solo Loop

It looks and feels similar to the silicone sports band, but with no overlapping parts. I set up my watch with a black size 4 strap that Apple provided and just slipped in on my wrist like a hair tie. The material feels stretchy and slightly smooth to the touch. I thought it felt a bit tight at first, but I barely felt it on my wrist after a few hours. It is important to get your size right though, because the size down for me would've been way too small. 

This will require you to measure your wrist before you buy it. And for this you'll need a measuring tape, which I personally don't always have on hand. It's also expensive for a band that I'd worry would stretch a bit over time. It's $49 on its own, the same price as the silicone sports bands. 

Gabriel Sama/CNET

I'll have to report back on the stretching once I've used it for a while. I do think it would be a good alternative for kids, which Apple is now targeting with its new Family Setup, because it's less cumbersome to put on and take off.  

The new Family Setup feature allows you to set up a second Apple Watch that doesn't need its own iPhone . You can program location alerts from the parent's iPhone, designate which contacts they can communicate with and limit use during certain hours with the School Time mode.

There are also new ways to customize the watch face with a new Animoji and Memoji that you can create directly on the watch, which I did. I don't know how long I'll keep it on as my main screen, but I can see this being popular with kids too. 

Faster processor, but only slightly better battery 

The other key upgrade to the Apple Watch Series 6 is the faster processor: Apple's S6 chip is based on the A13 Bionic chip found in the iPhone 11 and 11 Pro . The Watch feels snappy loading apps, displaying messages and showing stats in real time. But the Series 5 already felt fast, and so far I haven't noticed a huge change in my day-to-day use. The Series 6 is also the only Apple Watch to include Apple's new U1 chip for ultrawideband support, which improves spatial awareness between devices. The benefits of this new U1 chip may not be obvious right away, but eventually will enable features such as CarKey, which allows you to use your device as a key fob.

I also haven't noticed much of a change in battery life compared to the Series 5, which is disappointing -- now the Apple Watch can track your sleep, you'll want to use it 24/7. The silver lining is that it's now better at managing battery life during certain workouts and it exceeded Apple's 18-hour claim in my testing. 

Vanessa Hand Orellana/CNET

The Series 6 can last up to seven hours on a single charge during an outdoor run, up from six hours on the Series 5. Though I have not tested this out for myself yet, I did notice that the Series 6 had more battery left after a 30-minute outdoor jog compared to my Series 5.

Even on the days I took it for a GPS-only run without my phone in tow, I still ended the day with the 30% charge needed to track my sleep. I could even squeeze in a couple extra hours in the early morning. You can also disable the always-on display if you want even more battery, which is not an option on any of the other models. 

The Apple Watch Series 6 and Apple Watch SE will charge to 100% in 90 minutes compared to the two-hour charge time of their predecessors, which helps speed your day along. But sometimes my morning routine wasn't long enough for it to charge back up to 100% and I ended up having to charge it in bursts throughout the day, which would be hard if you didn't have a charger on hand. And you better hope you have a wall charger at home, because Apple isn't including them in the box anymore. You just get the cable with the magnetic puck.

Bye-bye, Force Touch on WatchOS 7 

The update to WatchOS 7 eliminated Force Touch on the Apple Watch across the board, so instead of applying more pressure on the watch face, you now have to long-press to prompt an action. You still get the same haptic feedback that you would with Force Touch, but it didn't seem quite as satisfying. It also means you have to relearn certain actions like switching from grid view to list view for your app screen. If you long press on the app page, they all start to jiggle like on the iPhone to rearrange or delete. The list view option has moved to the Settings. 

Real-time elevation and cardio fitness alerts 

The entire Apple Watch line will also get new fitness features with WatchOS 7, including dance tracking and core training, but only the Series 6 and Apple Watch SE include a new always-on altimeter that provides real-time elevation monitoring you can use during an outdoor workout. 

The Apple Watch also uses the Vo2 max reading (maximum oxygen consumption during exercise) to monitor cardio fitness levels. It will eventually let you know when your levels are too low with a new notification feature that's launching later this year. According to Apple, this metric can be an important indicator of overall health.

Watch this: Apple Watch's new Family Setup plan is for kids

Fitness Plus with the Apple Watch at its core

Apple's new subscription Fitness Plus service brings guided workouts to the Apple Watch, iPhone, iPad and Apple TV . You can choose from a variety of different programs to stream on your device of choice and sync with the Apple Watch. The Apple Watch will automatically start the correct workout for you and display your stats on the screen, so you can follow along without having to glance at your phone. Instructors will use the Apple Watch as a training tool to push you during a workout. 

Sadly I wasn't able to test this out on the watch yet, because it's not launching until later this year. The Fitness Plus subscription will cost $9.99 (£9.99, AU$14.99) a month, or $80 (£80, AU$120) a year.

Still the best smartwatch, but with more competition 

The jury's still out on whether blood oxygen tracking becomes a must-have feature, but with the Series 5 discontinued, it's now your only option if you want that always-on display and ECG app. Those are big selling points for the Series 6 and I personally would have a hard time going back to a screen I had to raise to wake. The question now is whether that's going to be enough to sway people to spend the extra $130 when they now have a compelling alternative in the Apple Watch SE, which shares many of the same features for less.  

Read more: Apple Fitness Plus vs. Peloton: Which streaming workout service is better?