Fitbit Sense Review: Healthcare via your smartwatch

The smartwatches Fitbit Sense, Versa 3 and its predecessor, the Versa 2 (still available), all from Fitbit, have very similar dimensions. Instead of the mechanical button of the Versa 2, the Sense and Versa 3 watches are now equipped with a sensor button that is integrated into the aluminum case, similar to the Charge 4. The Versa 3 also has GPS. Another difference is that only the Sense and Versa 3 will be equipped with Google Assistant by the end of the year while the Versa 2 will not.     

All three wearables measure the heart rate and oxygen levels in the blood (SpO2). Only the Sense has additional sensors with which it can assess ECG and electrodermal activity (EDA). It also has a sensor that measures skin temperature.

Other hardware include a speaker, a microphone, a voice assistant and NFC for mobile payment. You will have to check whether your bank supports Fitbit Pay. Alternatively, Fitbit also offers its own Fitbit Visa Card.    

The Sense could be a bit faster occasionally. For example, you have to wait a good 5 seconds before anything happens when opening the Today dashboard that displays the daily sleep and activity data.

The Sense monitors the user's heart rate 24/7 and emits warnings when limits are exceeded or dropped below, according to Fitbit. We checked the precision of the device's heart rate sensor by comparing it to a chest strap from Polar. There weren't any major differences between the two results. The heart rate sensor remained accurate within 1-3 beats compared to the belt in our test with an increased heart rate, which we simulated in performance mode. Those are promising results.

The Fitbit Sense logs changes to skin temperature and can also create an ECG (electrocardiogram). Fitbit received the EU's CE certification (Conformité Européenne), which is important for medical devices, in September. To do an ECG, you have to place your index finger and thumb on the stainless steel ring around the display for 30 seconds. If the Sense recognizes any heart rhythm irregularities, this could indicate atrial fibrillation, which doctors connect to an increased risk of stroke. 

Another feature is the EDA scan, which detects electrodermal activity of the skin. If the Sense registers changes in the skin's electrical conductivity during a 2-minute scan, this can indicate emotional stress. The test is conducted at rest, which in itself can reduce the heart rate. This effect can be enhanced with relaxation exercises through Sense and the Fitbit app.

The hemoglobin in our red blood cells plays an important role in supplying our body with oxygen. The oxygen level in our blood stream (SpO2) indicates, to what percentage the hemoglobin in the lung is filled with oxygen. This value usually lies between 90 and 100 percent.   

Fitbit doesn't measure this saturation manually at the press of a button, like the Huawei Watch Fit oder Honor Watch ES do. Instead, it is active during the night while you sleep.

The oxygen saturation curve in the sleep protocol doesn't just show the trend of proportional saturation, it also indicates the deviation from your own body's average. High deviations could indicate sleep apnea. The paid Fitbit Premium subscription also gives you access to the heart rate trend. Neither the app nor the Today dashboard displays the actual proportional saturation. At least the SpO2 watch dial displays your average. This is based on the measurements of the previous night and doesn't change during the day.

The Fitbit Premium monthly subscription costs around $10 and offers premium functions. The sleep protocol, for example, is complemented with a heart rate diagram. The following screens display the sleep protocol without a subscription. The four screens below show the same sleep protocol with a premium subscription. Except for the estimated oxygen deviation, all diagrams can be opened to full screen on the smartphone.

Buyers of the Fitbit Sense can trial the premium subscription for free for six months. Apart from the additional diagrams in the sleep protocol, the subscription features additional health metrics about the development of oxygen saturation at night, the breathing rate, the heart rate variability and skin temperature. The subscription also allows users to participate in virtual competitions and create plans for health-related and athletic goals.

The Sense also has an app named "Coach" that features guided cardio and body workouts. Short video clips instruct the user what to do. At the start of the test there were three workouts available that ranged from between 7 and 15 minutes. The premium subscription offers a wider range of workouts.

The normal training app lists 20 training modes including running, bicycling, using the cross trainer as well as kickboxing, playing golf and doing interval training. 

You can personalize the trainings screen and set parameters such as track length for swim training or the number of repetitions, training duration, length of breaks and total duration of an interval training. The Sense vibrates differently when reaching the fat burning, cardo or high performance level, which is useful if you want to run within a certain heart rate range, for example. The Always On mode reduces the refresh rate but always displays the training screen. 

The sensor key pauses and restarts the workout while pressing a softkey on the display ends the workout. This worked well in our review, even with sweaty fingers, although the sensor key is more difficult to find and activate that the mechanical button is on the Versa 2. The Sense will only show you a summary of your workout right after it ends. After that, you will only be able to see your training metrics in the app.