I Wore the Fitbit Sense 24/7 for Two Months. Here’s What I Learned.
By: Thomas Smith
Tags: Gadgets, Wearables, Fitbit, Technology, Fitness

I Wore the Fitbit Sense 24/7 for Two Months. Here’s What I Learned.

Photo: Smith Collection/Gado/Getty Images

For the last two months, I’ve worn the Fitbit Sense smartwatch 24/7, only taking it off to charge it. Living with the watch on a daily basis, I’ve experienced its quirks and strong points and seen how it performs in the real world. I’ve taken it along on a grueling workout, used it to manage my pandemic stress, connected it to my microwave, and let it perform medical tests on my heart. Here’s what I’ve learned.

As I shared in my first-look review, the Sense ($329.95) is Fitbit’s most advanced smartwatch to date and the best health-oriented watch on the market. True to its name, the watch is riddled with advanced sensors, including a heart rate tracker, accelerometers, an altimeter, a blood oxygen (Sp02) sensor, a skin temperature sensor, and an Electrodermal Activity (EDA) sensor that measures stress levels and also serves as a medical-grade ECG.

All of these sensors feed data into Fitbit’s analytics algorithms, where they’re transformed into easily digestible metrics, graphs, and logs, all of which you can access on your phone (some are also available on the watch itself). The Sense knows how effective your workout was, how well you slept last night, how you’re coping with stress — even if you might have Covid-19.

At its core, the Fitbit Sense is a fitness product, and most users probably buy one to get more active. So I decided to start my extensive experiments with the Fitbit Sense by testing its workout-tracking features.

Or rather, I mistakenly stumbled into such a test. When I first ordered the Fitbit Sense, I told my personal trainer about it. He got a kind of gleeful look in his eye, and said “Great! I’ll design a workout that really puts it through its paces!” I immediately began to question the logic of telling my personal trainer that I had ordered the Fitbit Sense.

The next time we connected, my trainer delivered on his promise. Our workout began with stretching, then a five-minute sprint around a track at my local park. I then did three sets of a circuit consisting of weighted box-squats, lunges to step-ups on a concrete planter with a 12-kilo kettlebell, overhead presses, and burpees. The workout, my trainer told me, was designed to test static stretching, cardio, weight-bearing exercise, pushing/pulling, and explosive movements, so we could see how the watch handled each. Normally you’d focus on one of these types of exercises per workout session. In the name of science (and to the chagrin of my body), we did all of them at once.

The Fitbit Sense can track a variety of workouts, from walking to kickboxing. You initiate a workout on the watch itself through the Exercise app and select the kind of workout you plan to do. Depending on what you choose, the watch will use a different set of sensors to track and document your movements and will display stats tailored to the kind of workout you’ve chosen.

If you’re going on a hike, for example, you can select the Hike setting, and the Sense will show how many steps you’ve taken and the distance you’ve traveled. It will also use its onboard GPS to track where you go and provide you with a map afterward in the Fitbit app.

Mapping a hike on the Fitbit Sense.

If you select a static workout like weightlifting, on the other hand, the watch will disable its GPS and tell you about your heart rate zones and calories burned instead.

For a workout like mine with multiple components, I selected Circuit Training. This is a good general setting to track a workout that blends multiple elements. The watch monitored my movements throughout the approximately 45-minute session and provided summary statistics and charts in the Fitbit app on my phone when I was done. A chart of my heart rate shows how the watch captured my workout.

My heart rate stayed steady during stretching, before rocketing up during the sprint to a max of 180 beats per minute, which is just below my personal peak of around 195. It drops as I cool down from the sprint (with a little bump as I jog back to my starting point), before going progressively higher as I do the box squats and lunges to step-ups. It then drops again as I do overhead presses (a strength-based pushing exercise that’s less cardio-intensive). Finally, it jumps again as I do the murderous, cardio-intensive burpees. The pattern repeats almost exactly for each of my three sets — you can clearly see the three sets as nearly identical patterns of heart rate changes on my graph.

Reviewing the graphs and stats, my trainer and I agreed that the watch did an admirable job of tracking my workout. We also agreed that we hated the experience of exercising with a smartwatch.

To me, workouts are all about being present in the moment, developing a better understanding of what you’re able to do physically (and ideally expanding that over time), and focusing intensely (almost meditatively) on the basics of movement, form, and flow. It’s about training your mind just as much as training your muscles.

It’s hard to achieve a flow state when you’re constantly futzing with a tiny screen on your wrist. Wearing the Sense, I found that I was always stopping to check my heart rate, shift the watch around so the kettlebell wouldn’t crush it, and investigate mysterious buzzes and vibrations that it seemed to send out at random as I exercised. I also found that the Sense mostly told me things I already know. Sprints are cardio-intensive. Burpees are hard. Moving burns calories. I don’t need a $329 gadget to tell me those things.

Where the watch was most helpful, I found, wasn’t for formal workouts — it was for the days where I didn’t do structured exercise. The Fitbit Sense monitors your movements 24/7. There were plenty of days during my testing where I’d glance down at my wrist in the evening and realize I’d only done 3,000 steps for the day. That provided the motivation (or electronic guilt trip) to stand up and move more, getting closer to my 10,000-step goal.

That’s the biggest advantage of a fitness watch like the Sense--you’re getting “credit" for all your movements throughout the day, not just the times you’re actually working out. Increased mindfulness of your movements (or sloth) can be a powerful motivator to take the stairs, park farther away, and otherwise add more steps into your daily routines. Fitbit even has a feature that reminds chair-bound remote workers to stand up and walk around once per hour, which feels like a very 2020-friendly feature.

The Fitbit Sense adds some other pandemic-friendly features, too. Most notably, the watch includes a suite of advanced sensors and features to measure stress, which it tracks as a daily Stress Management score between 0 and 100. Fitbit’s stress tracking takes a holistic approach, factoring in sleep data (more on that later), exertion balance (whether you’ve exercised too much or not enough), heart rate variability, resting heart rate, and your own self-reported stress levels. It also includes readings from the watch’s onboard electrodermal activity (EDA) sensor, which measures tiny changes in your skin’s conductivity to determine how physically stressed you are.

EDA readings don’t happen automatically — you have to decide to sit down and take one. To do so, you place your hand on top of the watch (the EDA sensor is embedded in the bezel around the watch face) and keep it there throughout the EDA session as the Sense takes stress readings. Sessions last a minimum of two minutes, but you can go for up to 60 if you want. The session begins with the advice to “Calm your mind and just breathe.”

When I first tested the watch, that really pissed me off. Calm my mind? Breathe?? It’s 2020. There’s a damned pandemic on, wrist computer! Somehow “just breathing” doesn’t seem sufficient to address the collective, bizarre challenges 2020 has wrought on the world. Wired’s Adrienne So felt the same way, noting the irony of being told to breathe while in the midst of historic wildfires, which made California’s air quality among the worst in the world. I was also confused by the format of the EDA results. I was expecting some kind of metric for stress levels, but the results are shown as a bar graph of EDA “responses.”

Over time, though, I’ve come to really enjoy the Sense’s EDA sessions. I realized that Fitbit’s goal is not to show a snapshot of your stress levels at a specific point in time. Instead, they’re focused on giving you tools (like meditation, mindfulness, and yes, breathing) to reduce your physical stress — as well as metrics to show how effective those tools have actually been.

I like meditation, but I often find it boring. And I sometimes wonder whether it’s actually doing anything, or if I’m just sitting there and visualizing a glowing lotus flower for the hell of it. With feedback from the EDA sensor and the Sense’s heart rate tracker, you can set aside a few moments to meditate or relax in whatever way works for you (both pranayama breathing and progressive muscle relaxation have science behind them), and immediately see how effective your session has been. If you’re physically relaxing, you should see a decline in the number of EDA responses on your bar graph over the course of your session. You should also see a drop in your heart rate — the Sense displays your starting and ending heart rate whenever you complete an EDA session.

From my testing, I’ve found the sessions very effective. If I notice that my heart is racing (or especially if I’m having trouble sleeping), I’ll do a quick two-minute EDA session. I like that the Sense allows you to initiate these on the watch itself — if I had to pull out my phone to do a session, I know that would just add to my stress. If I focus on it, I find that I can reduce my heart rate by 20 beats per minute or more during a short session.

I often see a noticeable decline in my EDA responses, too, though this seems to depend more on how I’m feeling overall on a given day than on what I do during the session itself. I’ve even come to enjoy the little fortune-cookie mantras Fitbit displays after each session. I will ask myself one thing I’m grateful for right now! Thanks for suggesting that, watch! Yes, I understand the irony of applying metrics to a process like meditation, which is supposed to be all about letting go. But for me, knowing that my meditation or relaxation sessions are actually helping provides the motivation I need to do them consistently.

The Fitbit Sense adds other functions for tracking your overall health, too. The back of the watch includes a large conductive plate that measures your skin temperature while you sleep. In the Fitbit app, you can see if you’re above or below your temperature baseline each night, and track how your skin temperature changed throughout the night. Fitbit says in the app that skin temperature can change based on “room temperature, bedding, circadian rhythm, menstrual cycle or the onset of fever.”

My air conditioner unexpectedly died during California’s heatwave in October, so I can confirm that room temperature indeed causes changes to your resting skin temperature. For several nights in a row, my room reached 86 degrees at night, and this reflected as a 2.2-degree increase in my average skin temperature.

My AC died, and my skin temperature went up.

For users who are biologically female, Fitbit likely uses skin temperature to assist with tracking fertility (the watch also allows you to manually input core temperature readings).

And skin temperature is useful for something else, too — telling you if you might have Covid-19. Combined with data from the watch’s onboard blood oxygen sensor (SpO2) and other factors, Fitbit says that its watches are showing promise as tools for the early detection of Covid-19 infections and other illnesses. At the moment, Fitbit isn’t making these capabilities publicly accessible, but the company is working on further studies, with funding from the U.S. military.

One aspect of the watch is medically cleared, though — the Sense’s electrocardiogram (ECG) sensor. Using the same hardware as the EDA sensor, the Fitbit Sense allows you to take an ECG reading right on the watch. This function was only approved by the FDA about a week after the watch began to ship in September, so the ECG app isn’t installed on the watch by default. To get it, you have to take a questionnaire and then install it from the Fitbit app on your phone.

Taking ECG readings on the Sense is even easier than taking EDA readings. You open the ECG app, place your thumb and forefinger on opposite sides of the bezel, and sit perfectly still for 30 seconds.

The watch measures your heart’s electrical activity, and tells you whether you had a “normal sinus rhythm,” an “inconclusive” result (usually because you moved or spoke), or evidence of a potential heart arrhythmia. You can download a PDF showing a raw trace of your ECG results to send to your doctor, along with a description in medical jargon explaining why on earth you’re sending them a PDF generated by a watch.

For people with undetected heart conditions, the feature could be life-saving. Fitbit’s main goal with the feature is to detect atrial fibrillation (AFiB), a heart rhythm condition that can be hard to diagnose, in part because it can be intermittent, and doesn’t always show up on ECGs taken at your doctor’s office. By tracking your heart at home — especially if you notice a heart-related symptom, like fluttering or missed beats — you might be able to detect a hidden AFiB that your doctor missed. Thankfully, all my own ECG readings have been normal.

The inclusion of a real FDA-approved medical device on a smartwatch is a big deal for Fitbit. The company has been courting FDA approval to use the SpO2 sensors on its watches in order to detect sleep apnea for years. The Sense allows you to see your nighttime SpO2 reading using a special watch face, as well as in the Fitbit app. Mine generally stays between 92% and 96% at night. The feature isn’t medically approved yet, but now that Fitbit has gotten FDA approval for one feature, you can expect to see FDA-approved sleep apnea detection on the watch within a few years.

In my testing, I tried out several apps on the Fitbit Sense. They’re not great. Fitbit has always excelled at fitness and health tracking, but the company has never developed a large ecosystem of apps for its watches. The New York Times app is neat, but isn’t sized properly on the watch, so headlines get cut off. Fitbit Pay, which allows you to pay via the watch, is helpful when it works, but I’ve found that it only works about half the time on all the Fitbits I’ve used. Many users were upset when Fitbit removed the ability to load MP3s onto the watch — to use your Fitbit Sense for music, you now need to use either the Deezer, Pandora, or Spotify app.

The best non-fitness feature on the Fitbit Sense is the watch’s integration with voice assistants. Initially, the watch only supported Alexa. But with Fitbit’s recent acquisition by Google, the watch now supports the Google Assistant as well. Speaking to your watch seems gimmicky, but it’s actually extremely helpful. I often find myself adding an item to my Alexa shopping or to-do list from the Sense when I’m on the go. It saves having to take out my phone, unlock it, find the Alexa app, and load my list just to make a simple note.

The watch’s Alexa integration also allows me to start my Amazon Smart Oven using my voice, from across the room. Saying “Alexa, microwave tea” into your wrist and having your microwave start up feels very futuristic, even if it isn’t terribly practical. Integrating Alexa with my office lights and switching them off from the watch is neat, too, and can actually save a bit of time — especially since I don’t have an always-on Alexa device in my office, for privacy reasons.

As Google completes the process of acquiring Fitbit, the company’s devices will almost certainly get more and better apps. Google brings both oodles of cash and a robust developer community to the table. Once Fitbits are a Google device, the company will almost certainly pour resources into building out a more complete app store — if for no other reason than to compete with the Apple Watch.

The acquisition also means that Google will have access to all the data (medical and otherwise) your Fitbit Sense is gathering. This has privacy researchers, like those at the Mozilla Foundation, concerned. According to the Foundation, “Google is in the process of buying Fitbit. What does that mean? We don’t know quite yet.”

Google’s control of your Fitbit data might be a positive thing since Mozilla says Google has robust privacy and security procedures in place. But if the company uses health data to target ads, that may make some users uncomfortable. Google’s impending takeover of Fitbit is, at the very least, something to be aware of if you’re buying the watch or gifting it to others.

Overall, I’ve been extremely pleased with my Fitbit Sense during the two months I’ve spent wearing it. I probably won’t use it to track formal workouts. But if it gets me out of my chair a few extra times per day, that’s a win. I find its stress tracking useful, and have come to really love the EDA sessions. In 2020, anything that helps to manage stress — or even make you more mindful of the stressors you’re experiencing — is a positive. The watch’s medical monitoring functions seem well-developed, and it’s comforting to know that real medical organizations like the FDA have signed off on the efficacy of features like the Sense’s ECG.

If you’re looking for a fully-featured smartwatch with tons of useful apps, the Fitbit Sense isn’t that. But if you’re looking for a watch that’s genuinely helpful in tracking (and improving) your fitness and overall health (both mental and physical), the Sense is the best product in Fitbit’s lineup, and the best watch on the market right now.