Fitbit, an American fitness product company headquartered in California, is facing a lawsuit from a number of users who say that the firm's health tracking devices can't be trusted to monitor heart rates.
The users filed a class-action lawsuit in California claiming the Fitbit Charge HR and Surge models consistently misevaluated their heart rates during workouts.
"Plaintiffs and many consumers like them have experienced - and testing confirms - that the PurePulse Trackers consistently mis-record heart rates by a very significant margin, particularly during exercise," the lawsuit claims.
The Charge HR and Surge techs can cost between $150 and $250.
One of the plaintiffs, Teresa Black of Colorado, says that her Charge HR dramatically understated her heart rate during a work out session. She said her fitness trainer manually recorded her heart rate at 160 beats per minute while her the device indicated that her heart rate was only 82 bpm.
Meanwhile, a Fitbit spokesperson said the firm conducts internal studies to validate the performance of its activity and health tracking products.
"But it's also important to note that Fitbit trackers are designed to provide meaningful data to our users to help them reach their health and fitness goals, and are not intended to be scientific or medical devices," the statement said.