Review: Fitbit Sense

Fitbit has the worst luck. In the spring of 2020, it released an affordable, outdoorsy fitness tracker just as the ongoing Covid-19 pandemic forced many people to stay home. Late in the year it released the Sense, which has a new stress-management tool to help cope with—in my case—said pandemic, racial injustice, life-threatening wildfires and toxic smoke, and the disaster that is remote schooling.

I took the Sense’s stress test in a hotel room on the Oregon coast, where my family and I fled to briefly escape Portland’s hazardous air quality. I got a Stress Management score of 93. I found that to be remarkable, considering I was extremely stressed, not sleeping, panic-spiraling over my kids’ blackening lungs, had been trapped in my house for more than a week, and had eaten only French fries for the past three days.

A good fitness tracker doesn’t just have sensitive sensors that collect tons of data. It also displays that data in an easily digestible way and provides simple, actionable advice. While the Sense does measure new biometrics, like measuring your blood oxygen and taking your stress levels through electrodermal activity (EDA), I’m not sure it actually helps you.

Photograph: Fitbit

The Sense is a good-looking fitness tracker. The square face has gently curved corners, no inscribed "Fitbit" at the bottom, and a glowing AMOLED screen that shows images in well-lit, striking detail. As is the case with all of Fitbit’s trackers, it also comes with a staggering variety of accessories. I like the sports wristbands, but with the Sense I opted for the woven coral (which I would not recommend, as it showed dirt within a few days).

Fitbit also has a variety of proprietary faces and a bunch of well-designed, and less well-designed, user ones. Previously, you had to load a specific SpO2 face to check your blood oxygen readings, and only while you were sleeping. But Fitbit has since enabled sleep blood oxygen tracking on the backend, meaning you now don't need a specific clock face to track your blood oxygen. Congratulations, you get to keep your Memoji on your watch face instead! (I'm kidding. Take that Memoji off right now.)

The company also added new SpO2-specific faces to the app gallery, in case you want to keep checking your blood oxygen minute to minute.

The SpO2 face has a scale that lets you see at a glance whether you're getting enough oxygen while you sleep. Over a week, I never got a score below 94 percent, which both I and the Sense registered as "fine." It’s difficult to take an SpO2 measurement while you’re asleep, but I did cross-check with a fingertip pulse oximeter to verify that the Sense’s HR and SpO2 measurements were reasonably accurate, which they were.

Every other day or so, the Sense had trouble taking my SpO2 measurements, and even on days when it worked, it sometimes took several hours (on a Garmin, it takes minutes). Fitbit's representatives told me the Sense was tested across a wide range of skin tones, but optical sensors do have a history of malfunctioning with people who are not white.

Photograph: Fitbit

The Sense’s other new biometrics are stress measurements. Fitbit claims that electrodermal activity, or EDA, as measured by electrical pulses in your sweat, is a reliable indicator of stress. You measure your EDA by tapping to take an EDA scan and placing your palm over the metal bezel. The Sense will measure how many EDA responses you get in the span of two minutes.

There’s long-standing research to back this up. Skin conductivity has long been used in polygraph tests to measure arousal, along with heart rate and respiration. The Sense combines this EDA scan with nine other inputs, including activity and sleep quality, to give you a Stress Management score of 0 to 100. The higher the score, the better prepared you are to handle stress.

This seems like a very similar metric to the Oura Ring’s Readiness score or Garmin’s Body Battery, only you have to tap farther into the Fitbit app and into the Stress tile to get to it. And while EDA seems like a good way of measuring flight response while, say, watching Hereditary, it doesn’t seem to be great at gauging the long-term stress of living under multiple constant threats.

Unfortunately, I got to test how the Sense measured stress firsthand. Some days—for example, the day that some of our friends had to evacuate due to wildfires, I had a go-bag packed by the door as smoke crept into every crevice of our home, and several friends’ houses burned to cinders—I had 16 EDA responses, versus my normal one to 5.

But what about it? The Sense didn't have any useful tips except telling me to breathe, which was ironic given that our air quality was so bad. Even on days when my head was about to explode, my Stress Management score stayed over 90. Today, a normal day, my Stress Management score is 74 because I had a hard workout yesterday. The score seems only marginally related to stress or my ability to manage it. The only useful piece of actionable advice I got was seeing that my heart rate lowered by about 10 beats per minute every time I sat quietly through a two-minute scan. But you don't need a watch to tell you to sit down and close your eyes every now and again.

Photograph: Fitbit

The truth is, these new biometrics might not be made for you at all. Many public and private institutions are currently vying for your wearable data in the race to predict Covid-19 before an outbreak starts. It’s not hard to imagine that researchers will soon be clamoring for your blood oxygen and EDA responses.

If you can help others, that might make the Sense worth it for some people, but right now, the Sense seems like an overreach, especially if you find the SpO2 readings to be unreliable, like me.

Many of my favorite features, like Sleep Tracking and Fitbit Coach, also remain locked under Fitbit Premium. A Premium subscription costs $80 every year. Add in the $330 Sense hardware, and you've spent as much as an Apple Watch Series 6 costs. At that price, you should probably just get an Apple Watch (if you own an iPhone).

Updated January 2021: We've mentioned new features Fitbit added in a software update that rolled out in November 2020.