NEW YORK (FOX 5 NY) – An ongoing class action lawsuit against the makers of the wildly popular health tracking device known as Fitbit alleges the heart rate monitor on several models is off by a noticeable amount.

Attorneys who paid scientists at California State Polytechnic University say their findings show Blaze, Surge and Charge HR models are on average 20 beats per minute inaccurate during exercise, reported Forbes.

Heart rates were found to be more accurate while wearers were at rest.

According to the lawsuit, “Plaintiff Black was approaching the maximum recommended heart rate for her age, and if she had continued to rely on her inaccurate PurePulse Tracker, she may well have exceeded it, thereby jeopardizing her health and safety,” reported Mashable.

Fitbit has responded to the latest allegations which are part of a lawsuit that was launched in January.

“It was paid for by plaintiffs’ lawyers who are suing Fitbit, and was conducted with a consumer-grade electrocardiogram – not a true clinical device, as implied by the plaintiffs’ lawyers. Furthermore, there is no evidence the device used in the purported ‘study’ was tested for accuracy.

“Fitbit’s research team rigorously researched and developed PurePulse technology for three years prior to introducing it to market and continues to conduct extensive internal studies to test the features of our products. Fitbit Charge HR is the number one selling fitness tracker on the market, and is embraced by millions of consumers around the globe.”