Fitbit Lawsuit Questions Popular Device’s Heart Rate Monitor Accuracy

The makers of the Fitbit fitness watch are coming under increasing fire, with a lawsuit and study claiming that some of the popular activity tracking devices do not provide accurate heart rate readings. 

Fitbit, Inc. faces a class action lawsuit over the accuracy of the Fitbit Charge HR and Fitbit Surge wristband activity trackers, which were brought by a number of plaintiffs who say that the heart rate tracking component is inaccurate. Originally filed in February, the complaint (PDF) was amended recently to include data from a new study that appears to back up the claims.

Researchers from the California State Polytechnic University reported that both devices, which use what Fitbit calls “PurePulse” technology, are inaccurate and inconsistent. The Fitbit accuracy study (PDF) was commissioned by a law firm involved in the litigation.

The study compared hundreds of thousands of heart rate readings from both the Surge and Charge HR with time-synced electrocardiogram (ECG) readings. They found that during moderate to high intensity exercise, the Charge HR heart rate readings differed from the ECG by an average of 15.5 beats per minute (bpm) and the Surge readings differed by an average of 22.8 bpm.

“In addition to being inaccurate, the PurePulse trackers are also inconsistent,” the researchers found. “The PurePulse trackers do not accurately measure a user’s heart rate, particularly during moderate to high intensity exercise, and cannot be used to provide a meaningful estimate of a user’s heart rate.”

The Fitbit class action lawsuit, filed in federal court in northern California, accuses Fitbit of fraud and seeks to represent anyone who purchased the devices.

“Unfortunately for purchasers of the PurePulse Devices, Fitbit’s technology does not work as represented. As user experience and product testing confirms, these Devices do not accurately record heart rates, particularly during the intense workouts for which Fitbit markets them,” the lawsuit states. “Nevertheless, Fitbit, which encourages customers utilizing the Devices to speak with their doctor to determine healthy target heart rates, continues to market and sell the Devices to consumers while delivering inaccurate and unreliable heart rate data.”

The plaintiffs say that if they had known the devices were inaccurate, they never would have purchased them. The watches retail for between $130 and $150. Fitbit officials have denied claims raised in the lawsuit, as well as the findings of the study.