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I always knew that the heart rate monitors on my gym’s elliptical were a lot of hooey — there was no way I burned 300 calories in 20 minutes without break a sweat — but I’m saddened to read today that Fitbit, which rose to popularity a few years ago and seems to be worn by everyone and their mother, might be just as unreliable.

Fitbit consumers from Wisconsin, California, and Colorado, allege that the heart rate sensor in its 2015 Surge and Charge HR products measures heart beats inaccurately, with a “significant margin” of error. They claim the errors occur particularly during intense exercise sessions, and that Fitbit falsely advertised that the devices measure every heartbeat. One plaintiff claims that her Charge HR recorded a heart rate of 82 beats per minute, but when her trainer recorded her heartbeat with a different device, it registered at the much higher rate of 160 bpm. Yikes. That’s quite a big difference. When she complained to the company, they refused to issue her a refund. These plaintiffs seek injunctive relief and monetary compensation in the form of damages and “economic injuries” caused by “Fitbit’s misleading heart-rate claims.” Fitbit, meanwhile, claims that these allegations are without merit. They told Fortune Magazine:

Well, now I don’t know who to believe!

Fitbit stands by their assertion that their PurePulse technology tracks heartbeats better than most cardio machines found in gyms, as PurePulse continues its monitoring activity even when the user is not exercising. This makes sense: I once read that you burned a surprising amount of calories by simply doing basic household chores. (Though I may have misused that information to get out of working out for a few months — whoops.) PurePulse works by using LED lights to monitor blood flow through a user’s wrist, which all sounds very Blade Runner to me. Fitbit’s algorithms then determine heart rate. Similar technology can be found in the Apple Watch, along with other smartwatches and fitness trackers.

To be fair, Fitbit always clearly stated in their pamphlets that their gadgets are developed to generate data for wearers to track their health and fitness ambitions, and that these gadgets “should not be confused with definite medical or scientific devices.”

Either way, don’t let this news get in the way of your daily workout. Most fitness trackers are meant to be motivational, anyway. So go throw on those sneakers and grab that run — with or without your Fitbit.

(Image via Fitbit)