​Fitbit Sense smartwatch can tell when you're sick or stressed

Fitbit steps into the world of health
Product laydown photography for Fitbit Sense.
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Fitbit has unveiled the Fitbit Sense, the company’s first true health device with ECG, stress monitoring and a bevy of new medical sensors.

The Fitbit Sense represents a change for Fitbit, as it moves from fitness tracking to serious health monitoring – and the company’s work on the COVID-19 pandemic has seriously influenced its features.

The new biosensor core packs in PPG heart rate monitor using the new PurePulse 2 sensor, electrodermal activity sensor, temperature sensor, and can monitor breathing rates and sleep.

Like the Apple Watch Series 5 and Samsung Galaxy Watch 3 it’s aimed at alerting users to afib, low/high heart rate and sleep apnea. It also goes up against the Withings ScanWatch, which seems to be in permanent FDA limbo.

But the Fitbit Sense goes further than any consumer medical device we’ve seen, with a focus on stress, and on general wellness – with the ability to warn you when you’re coming down with a virus or infection.

Read on for a deep dive into the Fitbit Sense.

Fitbit Sense features at a glance

  • EDA
  • ECG
  • Temperature monitoring
  • 1.58-inch display
  • 336 x 336 pixels
  • Google Assistant and Alexa
  • GPS
  • 50m water resistance
  • 20+ sport tracking modes
  • 6 day battery life
  • Fast charging
  • Price:

Fitbit Sense: hardware and design

​Fitbit Sense smartwatch can tell when you're sick or stressed

The Fitbit Sense is essentially a Versa 3, but with a much more packed sensor array.

It uses an aluminium case to keep things light, and an improved AMOLED display. Like the new Fitbit Versa 3, it is equipped with a 1.58-inch display with a 336 x 336 pixel resolution

It’s waterproof to 50 metres and also features built in GPS.

Details on design are a little bare, so we’re working to clarify screen size, case size and other key details.

And here’s the key information on price and release date. The Fitbit Sense will cost and will be released in late September.

That means Fitbit’s most advanced smartwatch is also its most expensive, but dramatically undercuts equivalent Apple and Samsung devices.

Fitbit Sense: heart rate and ECG

​Fitbit Sense smartwatch can tell when you're sick or stressed

As hinted in the Fitbit Heart Study announcement, the company has added ECG to its smartwatch for the first time. The sensor is awaiting FDA approval for use in the US.

You can place your fingers on the corners of the Fitbit Sense case to take spot ECG readings.

The heart rate sensor has been upgraded, and PurePulse 2.0 now uses multi-channel sensing to create multiple heart rate readings, and machine learning to extract the data across channels to create a more complete look at your heart rate.

Fitbit says that by using machine learning to analyse multiple channels, it’s able to pick up details that are imperceptible to humans analysing the same data.

Heart rate and resting HR are all still tracked and presented in the usual way, but there’s now a focus on heart rate variability (HRV) for the first time.

All devices, Fitbit included, use HRV as part of analysis, but for the first time Fitbit is presenting the raw dat to Fitbit Premium users.

A drop in the time between heart beats can show the body is under physiological stress, and it makes up one of the metrics that can be a red flag for possible infection.

Fitbit Sense: stress tracking

​Fitbit Sense smartwatch can tell when you're sick or stressed

Fitbit Sense is focused heavily on stress monitoring and aims to assist users in the detection and combating of stress.

Part of the new biosensor core is an electrodermal activity (EDA) sensor, which reads the moisture in the skin – combined with heart rate variability (HRV), temperature and other factors, to produce a single stress score.

Presented just like the sleep score, and plotted daily, Fitbit’s stress score offers a single indicator of your daily stress between 1-100. The higher the number the better your score.

You can also take a spot score in the EDA app, by placing your palm across the face of the watch.

Fitbit will also ask you to log how you are feeling, which will be mapped against the physiological sensor data.

And finally, Fitbit will offer up guided stress relief sessions from the app.

It’s a very different approach to stress than we’ve seen from the likes of Garmin, and more geared to the psychological effects of stress.

Many stress detection devices have focused on telling you your body is under stress – which generally means you’ve over exercised.

So it’s interesting to see how well Fitbit can map the data from its EDA sensor to how users feel. And more importantly, can it make you feel better?

Fitbit Sense: wellness and illness detection

​Fitbit Sense smartwatch can tell when you're sick or stressed

The addition of a temperature sensor on the Fitbit Sense has been born out of the COVID-19 trials by the company and is a step towards informing you that you could be coming down with an illness.

Temperature is logged at night so you can get regular and comparable baseline data, and spikes in body temperature can be a sign that something is changing. However, you can't take a spot reading.

Fitbit couples this data with information on breathing rate, blood oxygen levels, heart rate variability and resting heart rate in a new Fitbit Premium dashboard.

Changes in this baseline can show that something is happening in your body, although Fitbit stops short of prosaic warnings that an illness is occurring.

Fitbit’s COVID-19 studies showed that its devices could detect an infection 24 hours before the onset of symptoms, and that in some cases changes could be detected up to five days before getting sick.

Likewise, Fitbit said in its press conference that the menstrual cycle could be detected in body temperature changes – although these are not explicitly linked in the app.

Fitbit Sense: smartwatch features

​Fitbit Sense smartwatch can tell when you're sick or stressed

With all these medical grade features, it’s easy to forget that Fitbit Sense is also a smartwatch.

Like the Versa 3, it also gets 50 metres water resistance and GPS for the logging of workouts, and naturally heart rate tracking through those.

It uses Fitbit’s Active Zone Minutes and also generates Cardio Fitness Score (Fitbit’s demystified version of VO2 Max) to offer insights into your fitness.

Notifications are still delivered to the wrist, and there’s also music control – although Spotify offline playlists are still not supported. You can add MP3s.

Early verdict

This launch from Fitbit has us excited, and it feels like the kind of device we’ve been waiting for since we started Wareable in 2014.

While we’ve seen exciting medical features on the likes of Apple Watch and Galaxy Watch 3, this feels like it could be the first mass-appeal health watch.

While smartwatches have broken ground in detecting illnesses like afib and sleep apnea, a device that offers insights into stress and general illness is something new. And something everyone can relate to.

How we test

James Stables


James is the co-founder of Wareable, and he has been a technology journalist for 15 years.

He started his career at Future Publishing, James became the features editor of T3 Magazine and T3.com and was a regular contributor to TechRadar – before leaving Future Publishing to found Wareable in 2014.

James has been at the helm of Wareable since 2014 and has become one of the leading experts in wearable technologies globally. He has reviewed, tested, and covered pretty much every wearable on the market, and is passionate about the evolving industry, and wearables helping people achieve healthier and happier lives.

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