FitBit sued over claims of misleading heart rate tracking

FitBit's heart monitoring devices are called "wildly inaccurate" in a lawsuit accusing the company of false advertising.

Devices sold by the leading maker of fitness trackers "are mis-recording heart rates by a very significant margin" while on the brink of causing health risks for users, according to a complaint filed this week in a San Francisco federal court.

FitBit devices have been accused of mis-recording heart rates.
FitBit devices have been accused of mis-recording heart rates. Photo: Supplied

A Colorado woman alleges that her Charge HR device under-reported her actual heart rate by 50 per cent, as recorded manually by her personal trainer after a period of intense exercise.

"Scores of customer complaints confirm these are not isolated incidents," according to to the complaint, which was brought as a class action on behalf of other customers.

FitBit defended its products, pointing to internal studies verifying their accuracy.

"We do not believe this case has merit," Heather Pierce, a spokeswoman for the company, said in an email. "Fitbit stands behind our heart rate technology and strongly disagrees with the statements made in the complaint and plans to vigorously defend the lawsuit."

Fitbit, which had an initial public offering in June, remains the top seller of wearables, though its market share tumbled to 22 per cent in the third quarter of 2015 from 33 per cent a year earlier, according to market research firm IDC.

While rising competition may continue to chip away at its lead, analysts say design is more likely to determine consumer behavior than technology.