How Does a Fitbit Work?

They're all the rage but how do they tick?

A woman running.

Artem Varnitsin/EyeEm/Getty Images

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Fitbit is a company that makes a range of fitness bands, smartwatches, and accessories that you can use to track your steps, exercise, heart rate, weight, and more. The company also has mobile apps for iOS and Android and an in-browser dashboard where you can view your progress over time and manually log workouts. So how do they work and are they worth buying?

What is a Fitbit?

Fitbit has products in two main categories: smartwatches and fitness trackers, as well as some accessories. The company is most well-known for its fitness bands of which there are four lines: Charge, Alta, Flex, and Ace.

Fitbit Charge 3 fitness band in black

The Fitbit Charge line is the most advanced (and highest priced). It ships with two bands, in size small and large, and comes in a few colors. Some special edition Charge models support Fitbit Pay, the company’s mobile payment app. Charge fitness bands have features including a touchscreen, smartphone notifications, activity and health tracking, automatic exercise detection, and water resistance so you can take it for a swim.

The Alta HR is almost as advanced as the Charge. It comes with a built-in heart rate monitor (that’s what the HR stands for), and it tracks sleep. You can get notifications on the band for calls, texts, and calendar reminders too. The Alta fitness band has less advanced sleep tracking and lacks a heart rate monitor, but otherwise shares the same features. Neither Alta fitness band is water resistant enough for swimming.

The Flex band is probably the most well-known Fitbit (and lowest priced). It’s swim-proof so that you can track your laps, has automatic exercise recognition, and displays call and text notifications.

Finally, the Ace fitness band is made for kids eight years and older. It’s a tiny device that attaches to a wristband and tracks steps and physical activity and can display incoming call notifications if connected to a smartphone. The Ace is splash-proof, but not swim-proof, so a child can wear it in the shower, but not in the pool.

Fitbit has two lines of smartwatches, Versa and Ionic.

Fitbit Versa smartwatch in black

The Ionic, released in 2017, has a touchscreen, built-in GPS for fitness tracking, and sleep and calorie tracking. The watch is also water resistant to 50 meters, so you can use it while swimming.

The Versa, released in 2018, has a slightly different design but shares most of the same features except for built-in GPS. To use GPS while exercising, you have to connect the watch to your smartphone.

Fitbit Pay is available on the Ionic and special editions of the Versa for mobile payments.

Accessories-wise, Fitbit has a smart scale (Aria) that syncs with the Fitbit app, wireless headphones (Flyer), and replacement wristbands.

How Fitbits Work and What Fitbits Do

While there’s an array of Fitbit products that do different things, the fitness bands and watches all track steps. Many can recognize common exercises, such as running and biking, and some can track swimming. You can then look at the Fitbit app to see your progress by day or by week and adjust your goals accordingly. If your Fitbit has GPS, you can also see a map of your route, pace, and elevation.

Fitbit app screen showing number of steps, miles, calories burned, and minutes of activity.

You can add Exercise Shortcuts on the app or the Fitbit.com Dashboard for workouts that aren’t automatically recognized, such as yoga. There, you can add goals for each exercise, based on time, distance, or calories burned. Then you’ll be able to start and end that workout on the fly.

Fitbit devices use an accelerometer to measure your movements. The accelerometer takes the movement data and translates it into digital measurements, which it how Fitbits count your steps, and measure the distance you’ve traveled, calories burned, and sleep quality.

For steps, Fitbits use an algorithm to look for motions that indicate a person is walking. If you’re driving on a bumpy road, this movement can register as steps, so be warned. For the best results for measuring distance and calories burned, make sure to measure your stride and log it in the Fitbit app, and keep your weight up to date.

The Fitbits that count floors — flights walked up — use an altimeter that detects whether you’re doing up or down. If you’re going up, it registers one floor for about every 10 feet you go.

What is Fitbit Pay?

Since Fitbit devices run on a proprietary operating system, they don’t have access to mobile payment platforms from other parties, including Apple Pay, Samsung Pay, and Google Pay. Fitbit Pay works with Android, iOS, and Windows phones, and is available in more than a dozen countries including the United States, Canada, Australia, Singapore, and a handful of European countries. You’ll also need to connect your account to a compatible bank; Fitbit keeps a running list on its website. At the register, Fitbit Pay works similarly to the competition.

Fitbits vs. Smartwatches

Some smartwatches do all or most of the above including the Apple Watch, Samsung Galaxy Watch, and models that run Wear OS (formerly Android Wear). Generally, these watches are quite a bit more expensive than a Fitbit fitness band and even more than Fitbit’s Ionic and Versa smartwatches.

However, Fitbit’s smartwatches have access to fewer apps than Apple, Samsung, and Wear OS watches, since it runs on the Fitbit OS. Also, the interface looks at acts differently from the one running on your smartphone. There are limitations in how you can interact with notifications. More advanced smartwatches let you do a lot without having to take out your smartphone, including responding to messages and even answering phone calls (LTE models only). Like Wear OS smartwatches, Fitbit OS watches are compatible with both Android and iOS. When it comes to mobile payments, Fitbit watches work with Fitbit Pay, while the others work with Apple Pay, Samsung Pay, and Google Pay, respectively.

Think of Fitbit smartwatches as the lower cost entry-level device compared to the big guys. If the price tag is too high on the more advanced smartwatches, consider giving a Fitbit smartwatch a try to see if you even like wearing a smartwatch.