Fitness tech companies, particularly Fitbit and Garmin, want to monitor the level of oxygen in your blood. It's a metric that could help spot signs of sleep apnea and other breathing-related problems, so companies have been scrambling to perfect their SpO2 sensors and incorporate this data into their ecosystems in a meaningful way.

Fitbit still hasn't activated its SpO2 monitors in its wearables (although that feature should roll out in beta in November), but Garmin has. Its newest fitness tracker, the $129 Vivosmart 4, includes an SpO2 monitor and measures Body Battery, which lets you know when you should plan your next intense workout session and when you should take a rest day.

Those two features, in addition to an all-new design and an affordable price, attempt to push the Vivosmart 4 above the rest of the fitness tracker crowd. As we saw with Fitbit's Charge 3, trackers have fallen into a boredom trap as of late, so companies are trying to find unique ways to capture the attention of potential customers who aren't fully sold on smartwatches. While Garmin achieves a certain level of differentiation with the Vivosmart 4, it's unlikely that everyone who prefers fitness bands to smartwatches will gravitate toward this device.

Design

Garmin consistently one-ups itself when it redesigns wearables from scratch. The Vivosmart 4 is leaps and bounds more attractive than the Vivosmart 3, which was an unnecessarily bulky band. Garmin shaved off 3mm from the new device's width and nearly 1mm from its thickness. That, combined with the lightly textured silicone band, the new 0.26×0.70-inch OLED display, and the striking aluminum bezels, make the Vivosmart 4 feel like a totally different device, rather than just the next in the Vivosmart line.

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It's the most comfortable Garmin device I've ever worn thanks to the updated design and its new 0.6-ounce weight. Unless you secure the band too tightly around your wrist, you won't feel the Vivosmart 4 when you're wearing it. Since it's safe to swim and shower with, you may forget it's on when you go to do one or both of those activities.

But like the Vivosmart devices to come before it, the Vivosmart 4's module is stationary in the middle of the continuous piece of silicone that makes up its band. You can't change the bands out, so you'll be stuck with the color you initially choose. That restriction will hurt Garmin (and probably already has), because most other trackers like those from Fitbit allow users to switch bands out for new ones. Not only does that increase the longevity of the device, but it also lets users feel like they're wearing a customizable accessory rather than an electronic device.

In addition to the standard array of activity-tracking sensors, the Vivosmart 4 includes an SpO2 monitor to measure blood oxygen saturation. We'll get into the details of this data in the next section, but the Pulse Ox sensor (Garmin's name for its SpO2 sensor) is a great addition to such an affordable device. Garmin previously only included it in its Fenix series of smartwatches, all of which are much more expensive than the Vivosmart 4. But the Vivosmart 4 is much easier to wear all day and all night than any Fenix watch, making it an ideal device to monitor breathing and oxygen levels during sleep.

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

Fitness: Body Battery, SpO2, and more

Body Battery

The two stand-out features of the Vivosmart 4 are Body Battery and SpO2 monitoring. The former quantifies everything that both drains and powers your body, giving you a score that shows how much "battery" your body has throughout the day.

Body Battery takes stress levels, heart rate variability, and sleep and activity data into account when adjusting your score—an intense morning workout could deplete your Body Battery by 20 or 30 points, but a restful period after that could increase it by 15 points. The score constantly changes throughout the day as you do different things, and at the end of the day, you can see the highest and lowest Body Battery scores you achieved.

I found Body Battery to be the most interesting for me when it changed due to stress. Garmin devices recognize stress through your heart rate—a pulse that's elevated for long periods of time (when not exercising) shows signs of stress. These stress periods can lower your Body Battery just like exercise can, although you likely won't see a 30-point loss from stress unless you were experiencing a tragedy.

In the Body Battery page in Garmin's Connect mobile app, you can toggle between the overall Body Battery graph and stress data. It puts stress into perspective because it shows exactly when your pulse spiked throughout the day. The Vivosmart 4 considered me "stressed" during a few pockets of my day, many of which were right when I woke up and was rushing to get ready for work or the gym. While I may not consider myself stressed during those times, it's illuminating to see just how often my pulse spiked throughout a normal day.

Those new to daily activity will get the most out of Body Battery. It can be difficult to assess your body's state when you're just starting to incorporate daily exercise or more intense workouts. Body Battery can help those users see how much their workouts affected their bodies, as well as how other factors like stress did, that they may not take into account on their own. That knowledge could help new users make more informed decisions about training days, intensity levels, and rest periods.