Fitness trackers are inaccurate and mislead users by over-estimating the number of steps users take, a new report claims.

According to research from the University of British Columbia, published in the medical journal JIMR Health, the devices have a habit of registering steps while users are performing other tasks.

“Consistent evidence indicated that Fitbit devices were likely to meet acceptable accuracy for step count approximately half the time, with a tendency to under-estimate steps in controlled testing and over-estimate steps in free-living settings,” the researchers said.

They added that consistent evidence indicates that Fitbit devices are unlikely to provide accurate measures for energy expenditure in any testing condition.