Fitbit Slapped With Class Action Lawsuit Over Heart Rate Accuracy


Fitbit has been named in yet another lawsuit, this time in the middle of the CES conference as it launches a new product line and works to keep consumers excited about its offerings. Unlike the last several suits, its newest legal troubles are not coming from a competitor, but rather its own customers. Fitbit was named in a class action lawsuit filed in the Northern District Court of California this week, with plaintiffs alleging that its heart rate sensor is unable to accurately record heart rate during intense physical activity, despite marketing materials that claim it can.

Fitbit relies on an LED-based optical sensor that illuminates the capillaries directly under the skin and then counts the change in capillary size as the heart beats. It’s a method that is widely adopted in the fitness tracker industry, with Basis, Samsung, and Apple all including the technology in their wearable devices. Optical sensors can be accurate under the right conditions, but to accurately capture real-time heart rate readings during periods of intense activity, a chest strap-based heart rate monitor is far more accurate. CNET hired Kaiser Permanente cardiologist Jon Zaroff, MD to evaluate the accuracy of heart rate sensors found within a group of fitness trackers and concluded that optics-based sensors were only reliable at a resting heart rate. Zaroff explains that by the time blood gets to the wrist, it has already slowed down. This does not impact accuracy when heart rate is below 100 BPM, but as a user’s heart rate climbs, wrist-based sensors will struggle to maintain an accurate reading. As a result, most fitness tracker manufacturers carefully word the marketing material that goes out with new products.


In the complaint, plaintiffs cite Fitbit marketing materials produced for its Charge HR and Surge fitness trackers, both of which utilize LED-based optical sensor technology to measure heart rate. In its marketing materials, Fitbit promises “continuous, automatic heart rate monitoring right on your wrist” and invites users to “check real time heart rate to ensure you’re working out at the right intensity.” While Fitbit’s heart rate monitor will accurately measure resting heart rate, its ability to keep up during strenuous exercise is questionable.

The case will have to overcome Fitbit’s standard arbitration clauses before it can move forward as a class action suit, but once it does, Fitbit could have a difficult time defending its marketing materials. To make matters worse, Fitbit’s newly unveiled Fitbit Blaze includes the same optical sensors included in its Charge HR and Surge trackers.

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