Fitbit, Inc., a manufacturer of wearable health technology, is involved in a national class action lawsuit filed on January 5, 2016 in the Northern District of California over two of its wristbands, the Charge HR and the Surge, based on their “PurePulse” LED-based technology used for tracking heart rates.

Generally, the lawsuit alleges that the heart-rate monitor used in those wristbands, advertised under the now amusing tag line “every beat counts,” does not monitor heart beats correctly. This allegedly especially occurs during times of intensive exercise.

In a statement to ArsTechnica responding to the lawsuit, a Fitbit spokesperson wrote, “We do not believe this case has merit. Fitbit stands behind our heart rate technology… [b]ut it’s also important to note that Fitbit trackers are designed to provide meaningful data to our users to help them reach their health and fitness goals, and are not intended to be scientific or medical devices.” Further, Fitbit released another statement after the lawsuit saying that “PurePulse provides better overall heart rate tracking than cardio machines at the gym.”

Fitbit is also involved in another class action lawsuit filed in May 2015 regarding its sleep tracking data, and is also involved in several suits against rival wearable-device maker Jawbone.