Fitbit Sense full review
The Fitbit Sense replaces the Ionic at the top end of the company's family of fitness and health smart-watches and activity trackers. On top of every Fitbit fitness metric and a built-in GPS, it measures your stress levels, skin temperature, blood oxygen, electrodermal activity, ECG, and heart-rate variations.
Update, June 2021: Fitbit reduced the retail price by £20/$30.
Fitbit calls the Sense an “advanced health smartwatch”, and it’s on health that it beats other Fitbits such as the Versa 3, which launched at the same time but focuses more on core fitness features. Read our Fitbit Versa 3 review.
It's a great smartwatch, only held back by what I consider a poor wrist strap and the fact that a few too many of the best health tracking features are reserved for paying Fitbit Premium subscribers.
Fitbit is continuing to add new features, such as the ability to take hands-free calls via the watch, which includes both a microphone and speakers, and adding Google Assistant alongside the Amazon Alexa voice assistant.
Design & build
The Fitbit Sense is a good-looking watch with a bright screen and a responsive user interface.
The main body is made of aluminium with a polished (medical-grade) stainless steel finish. This high-quality stainless steel ring is required to get some of the more advanced sensor readings. It’s also more durable; the medical-grade refers to its corrosion resistance.
It features a large 1.58in OLED display with a resolution of 336 x 336, which is bright, and easy to read even in direct sunlight.
The physical button found on the Versa 2 has been replaced with a new haptic sensor on the left edge - so there's no physical button to push in, but instead a touch-sensitive area that vibrates a little to let you know your touch has been recognised.
A standard button would have been easier, but really you can get wherever you need with a swipe.
Also new is the included swappable strap called the Infinity Band, and it takes a little getting used to. Instead of a classic watch strap, there’s a peg you push through the best hole for your fit, and then you close it through a loop.
This is my biggest gripe with the Sense: the band that it ships with just isn't as secure as the old watch-buckle. I had it fall off my wrist within 24 hours, and when you consider it's used in physical workouts, that isn't good enough. I would seriously suggest you purchase one of the accessory straps (the Sport one is great) that feature more robust buckles.
At least Fitbit has made swapping the bands much, much easier with the Sense. Changing the strap on the old Versa and Versa 2 was as fiddly as fiddly can get. This time, you just have to push a tab forwards and gently slide the strap off, and then click a new one in.
As for colours, the Sense is available in Graphite Stainless Steel with a Carbon band, or Soft Gold Stainless Steel and Lunar White band.
The Ionic, like the Fitbit Surge that it replaced, was marketed as a sports smartwatch. Sports was regarded as the pinnacle of the fitness tracker, but with the Sense Fitbit has pivoted away from sports to more of a focus on physical and mental health, as well as including all the expected fitness features.
Medical practitioners are increasingly warning that stress can be as dangerous as physical illness, contributing to high blood pressure, heart disease, obesity and diabetes. Fitbit has new tools in the Sense that can help identify stress, and therefore can potentially help you recognise and manage it.
Fitbit gives you a Stress Management Score that calculates how your body is responding to stress based on your heart rate, sleep, and activity level data.
It's helped by a new Electrodermal Activity (EDA) sensor that measures changes in the resistance of the skin to a small, undetectable electric current in response to sweat secretion. EDA measures the intensity of emotion, not its state, so an increase in conductance can be caused by both positive and negative emotional states. You can log your mood (stressed, calm, etc) after the EDA scan.
Users can then see a graph of their EDA responses in the Fitbit app, which tracks trends over time.
Some ways of managing stress include increasing physical activity and mindfulness - to which end the Fitbit app includes a guided meditation feature. After your session is over, prompts in the mobile app let you reflect on how you feel and see if these have a positive effect on your stress levels.
You can set a weekly mindfulness goal, track daily mindful minutes and days, and see trends. The score ranges from 1-100, with higher scores indicating your body is showing fewer physical signs of stress. It's paired with recommendations to better manage stress, such as breathing exercises.
Fitbit Premium members will get a detailed breakdown on how the score is calculated, which consists of over 10 biometric inputs, including exertion balance (impact of activity), responsiveness (heart rate, heart rate variability and electrodermal activity from the EDA Scan app), and sleep patterns (sleep quality). This will be a common theme as we go on, with some of the best tracking features in the Sense held back for subscribers.
There’s also a new skin temperature sensor, which can be used to indicate the onset of a fever or illness (can you think of any big ones going around?), as well as linking up with Fitbit’s existing health tracking for menstrual phases. This is done at night when the Sense will measure your skin temperature variation to see trends, so it doesn't display one-off readings.
It takes the Sense three nights to calculate your baseline skin temperature. You then see nightly average variation compared to that baseline temperature on the Temperature tile on the Today screen in the Fitbit app.
Other Fitbit smartwatches - Ionic or any Versa models - can also track your skin temperature, but only the Sense shows the data in the app without a Fitbit Premium subscription.
If your temperature is spiking or dropping compared to normal, this could be a sign of illness. Few of us use a thermometer every day, so it will be interesting to see if this works - though I'll have to wait for an illness to report back on its worthiness.
SpO2, ECG & more
Like other Fitbit smartwatches, the Sense can measure your average SpO2 levels - the amount of oxygen in your blood. This data can be used to detect your breathing rate alongside how well blood is being transported throughout the body. Low levels of oxygen can result in serious symptoms such as hypoxemia.
Note that the Sense only tracks your oxygen saturation levels while you sleep, unlike the Apple Watch 6 or Withings ScanWatch, both of which can take a blood O2 reading in just 15 seconds at any time of day. Check out our full comparison between Fitbit and Apple Watch for more on how the two brands stack up.
One complication is that the - unless you subscribe to Fitbit Premium - the SpO2 clock face must be set as your primary clock face when you are sleeping in order for it to track your data, which doesn't make the service as automatic as we think it could be.
A sensor in the Sense’s outer stainless-steel ring detects the electrical signals produced by your heart each time it beats, and a new electrocardiogram (ECG) app - approved by the US FDA and EU CE - can assess your heart for atrial fibrillation (AFib) heart-rhythm irregularity that can increase the risk of having a stroke, or normal, uniform sinus rhythm.
To take an ECG reading, you place your index finger and thumb on the opposite corners of the metal frame for 30 seconds.
There are three possible results: Atrial fibrillation (an irregular heart rhythm, so you should talk to your doctor for further tests); Normal sinus rhythm; and Inconclusive (if your heart rate is below 50 bpm or above 120 bpm, the ECG app will be unable to access your heart rhythm, so best not to take an ECG reading straight after having excellent aerobic fitness).
An improved heart-rate sensor helps to drive another new feature: heart-rate notifications when it detects that your heart rate is above or below your normal threshold. This can be useful to detect bradycardia (a heart rate that is too slow) or tachycardia (a heart rate that is too fast).
Fitbit Premium subscribers can see their heart-rate variation (HRV), the time between each heartbeat. Again, this can indicate the onset of illness, as well as fatigue and stress.
Fitbit's new Health Metrics dashboard goes into more collective detail on variation over time (7- and 30-day trends), tracking breathing rate (average breaths per minute), resting heart rate, heart rate variability (variation of time between each heartbeat), SpO2 levels (amount of oxygen in your blood) and skin temperature variation.
The company is keen to point out that users shouldn't regard this data as a medical fact, and should contact their doctor for professional advice.
Originally for Premium subscribers only, the Health Metrics dashboard has now been opened up to all users, at least for the 7-day trend view. The 30-day trend view is still for Premium only.
Read our full feature to learn more about all the Fitbit scores and measurements.
In the US the company has launched a new service called Fitbit Premium + Health Coaching. This gives subscribers virtual one-on-one access to a certified health professional and personalised plan using your Fitbit data, via the Fitbit app. The idea is to give you unlimited, appointment-free, actionable guidance to help you reach goals such as weight loss, stress reduction, or even managing a chronic condition.
As I've said, beyond the new health-tracking tech the Sense also has an impressive array of fitness features – indeed no other Fitbit has more than the Sense.
Of course, it tracks activities such as Steps, Distance, Floors Climbed, Active Minutes and Calories Burned.
The Active Minutes metric has been improved with the newer Active Zone Minutes (AZM) metric, and the Sense buzzes when you enter a new Heart-Rate Zone: Fat Burn, Cardio, or Peak. This gives you instant notice that you have reached a target zone, and whether you need to push harder in your workout or pull back. AZM was first seen on the Fitbit Charge 4, and has now been rolled out on most Fitbits, even the entry-level Fitbit Inspire 2.
The Sense can also give you real-time stats for over 20 exercise modes during your workouts. These can be set manually, or Fitbit’s SmartTrack tech can automatically recognise and record exercises such as running, cycling, swimming, treadmill, weights, yoga, and circuit training.
The Sense has GPS built-in, so you don’t need to lug your phone around with you on a run or bike ride. It also allows you, after outdoor exercise, to check your Workout Intensity Map in the Fitbit app to see your heart rate zones throughout your mapped route, plus distance and pace by kilometre or mile.
The watch also includes a 6-axis gyroscope to track strokes and laps while swimming. By contrast, the Versa 3 and most other Fitbits don't include gyroscope but instead calculate laps for swimming based on distance.
Like all the latest Fitbits, the Sense offers advanced sleep tracking, showing the light, REM and deep sleep stages and scoring you on the quality of your sleep based on your sleeping heart rate, time spent awake, and time in Sleep Stages.
Fitbit is still the clear winner on sleep measurement (duration and quality) in its battle with the Apple Watch, which is stymied by its much weaker battery life.
You can also get a sleeping heart rate measurement, but this is yet another feature kept back for Fitbit Premium subscribers only.
Battery and charging
Fitbit claims the Sense has a battery life of 6+ days, and I got nearly seven days on my first charge, although that was without using the GPS or Always-On Display function.
Of course, the battery life depends on your usage - using the GPS will burn through the battery faster than without. You can check the remaining battery life by swiping right or via the Fitbit app.
The Sense features a new charger type, which connects magnetically to the back of the Sense. I’d hoped it would connect any way round, but it fits in just one alignment. While I like the fact that it’s smaller than the chunky Versa charger, the fact that it lies awkwardly while charging is not so great.
It takes about two hours to fully charge from zero, though the company says that it takes just 12 minutes of charging to give you a day’s battery life using a new Fast Charging feature.
Software & apps
While the Fitbit smartwatches are no match for Apple or Samsung when it comes to running a wide range of apps, they do at least handle notifications well. Alerts for calls, texts and calendar events are supported, along with apps such as WhatsApp, Gmail, and Facebook.
Also handy are silent alarms that buzz on your wrist, in theory without waking your bed partner – although if used with a metal strap I can confirm that the buzz can be audible to others. Smart Alarm is a setting that lets you wake up at the best time during your sleep cycle (during light sleep), up to half an hour earlier but no later than the time you set.
In terms of apps you get the obvious - timers, weather, and a calendar, but also a meditation app and Fitbit Pay for contactless payments.
Spotify, Pandora and Deezer are there for music control, and you can also download apps for services such as Uber and airlines, along with other fitness and sport apps. There are still more apps on an Apple Watch, but the Sense will cover most of the essentials.
The 2.5GB of music storage would be great if you could use it with Apple Music or Spotify. Do you know anyone who uses Deezer or Pandora?
That said, the audio controls do work (unofficially) with Apple Music and Audible, for example.
The same goes for Fitbit Pay, which has limited bank support in the UK, although more if the US.
Phone calls from the wrist
Sense users can also take hands-free Bluetooth calls via the built-in mic and speakers, and send incoming calls to voicemail and control volume without reaching for a phone.
Phone calls on the Fitbit Sense work really well, as long as you aren't standing in a gale or near a pneumatic drill, with audio quality pretty good both ways, and the controls are easy to use.
Android users can also respond to text messages with voice-to-text commands - a feature sadly not available to iPhone users.
These features also work on the Fitbit Versa 3.
The Fitbit Sense also supports Amazon's Alexa, with Google Assistant out now in the US, UK, Canada, India, Australia, New Zealand and some other English-speaking countries.
With Google in the process of buying Fitbit it’s an obvious addition, as are the Android-only features like sending quick replies and voice replies right from your wrist when your phone is nearby.
Fitbit has now added the capability to receive audible replies from Alexa via the Sense's little speaker.
Price and availability
The Sense costs £279/$299/AU$449/CA$399. That makes it the most expensive Fitbit by some way - even the new Versa 3 is significantly less at £199/$229. Check out our Best Fitbit guide to see which other models we recommend, or find the latest Fitbit deals if you want to save a little.
If you want to get similar health tracking for less - at the cost of access to many of the smart features - it's worth considering the Withings ScanWatch, which offers even more comprehensive health features in a classic analogue watch design.
As you'd expect, there's also a range of straps and bands to go with the Sense. Accessory straps include woven and knit bands, silicone sports bands, and Horween leather bands. There’s even a range of Pendleton bands made from recycled plastic fibres.
And as I've already mentioned, to get the most out of the Fitbit Sense you'll really need a Fitbit Premium subscription - for better or worse. If you're new to Premium you'll get six months free with the Sense, but otherwise it will cost you £7.99/$9.99 per month.
We'd prefer Fitbit showed all its health metrics to all Sense users rather than restricting some to Premium subscribers, who would still get exclusive features in terms of extra onscreen workouts and meditation sessions.
The Sense adds a lot of new health features at the top-end of the Fitbit range. You could call it the hypochondriac’s smartwatch, it’s so full of warning signs, but there’s a lot here that will help indicate serious health problems that you will have the chance to improve.
Mindfulness might seem a little kooky to some and just a concern for those with too much time on their hands, but there is no denying that stress can affect us all, and managing it will quickly bring not just mental but long-term physical health benefits.
I do wonder how often you'll want to check your EDA or ECG if you're not suffering from a problem.
If fitness is all you want an activity-tracking smartwatch for, then the cheaper Fitbit Versa 3 offers everything you’ll get in that respect with the Sense.
For all-round physical and mental health tracking, the Sense is the Fitbit with it all.
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