(CNN)Your favorite fitness tracker may not be totally accurate, according to a study used in an amended complaint filed Thursday against Fitbit.
The class-action lawsuit, filed earlier this year, argues that the PurePulse technology used in the Fitbit trackers that measure your heart rate doesn’t do it as well as the company’s marketing material promises, a claim Fitbit denies. The technology is used in the more expensive models of the device, the Surge, Blaze and Charge HR.
The lawsuit was filed on behalf of people who bought these Fitbits specially to help them track their heart rate, whether for health reasons or to make sure they are getting the most out of their workouts.
“We are not arguing that it is a medical device. I think that is irrelevant,” said Jonathan Selbin, one of the attorneys who filed the lawsuit. “This is about the way they market it and that they charge a premium for the heart rate monitor, but it’s not giving a meaningful measurement.”
People who buy them, though, may have higher expectations.
Montoye says some people in his campus exercise program have complained that they went to the grocery store but didn’t get credit for their steps because they were pushing a cart. The device relies in part on a change in motion, and for the motion pattern to recognize a step, it must be large enough. Pushing a cart or even walking on a soft surface like a plush carpet may undercount your movement. It can also overcount your steps if you are riding on a bumpy road, according to Fitbit’s website.
Montoye said for participants who need to track their heart rate he advises using a different device that is more specific.
“If they had just been honest,” Selbin said, “and said it can give you a ballpark figure most of the time, or if the marketing emphasized that you can use these when you are aspiring to be healthier, that would have been OK, but that’s not how they market it, and they charge a premium for it.”
Fitbit was worth more than $8 billion right after it went public in June. The devices are enormously popular, with everyone from President Obama to Britney Spears and Ryan Reynolds spotted wearing them, so the lawsuit is bound to be watched carefully.
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