A number of users have issued a lawsuit against Fitbit, saying that the health tracking devices of the company can’t be trusted for monitoring heart rates.

CNET reported that the plaintiffs have filed a class-action lawsuit in California saying that the Fitbit Charge HR and Surge models have consistently underestimated their heart rates at the time of workouts.

The lawsuit claimed, “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”.

As per the lawsuit filed on Tuesday, the company has been accused under the suit, of defrauding its customers. It has asked for ‘an award of compensatory, monetary and punitive damages’. The Charge HR and Surge devices can cost between $150 and $250.

Teresa Black of Colorado, one of the plaintiffs, claimed in the lawsuit that her Charge HR significantly understated her heart rate when she was in a personal training session in June last year. She mentioned that her personal trainer recorded her heart rate manually at 160 beats per minute (bpm) whereas her Fitbit device showed that her heart rate was just 82 bpm in the normal range for a person at rest.

The lawsuit added that the Plaintiff Black was about to reach the maximum recommended heart rate for her age, and if she had been relying on her inaccurate PurePulse Tracker, she could have exceeded it, thereby endangering her health and safety.

The allegations have been clearly denied by Fitbit. The company said in a statement that according to it the case has no merit. Fitbit is quite confident about its heart rate technology and has strongly disagreed with the statements mentioned in the complaint. The company is looking forward to vigorously defend the lawsuit.