Did you find a fitness watch under the tree this year? Enjoy your new accessory—just don’t count on it too much if losing weight is one of your New Year’s resolutions. A study from the University of Pittsburgh found that participants who wore wearable devices and used an accompanying Web interface to monitor diet and physical activity lost significantly less weight than those who kept tabs on their diet and activity through a website alone.

SEE ALSO: Can Your Fitness Tracker Save Your Life?

“Both groups lost some weight because they restricted calories and increased physical activity, but the ones who lost the greatest amount were more self-aware about their behaviors,” says Claudio R. Nigg, Ph.D., director of the Health Behavior Change Research Work Group at the University of Hawaii, who was not involved with this study. “Having the device gather all of your data may mean you’re not processing the information in the same way—so you end up overestimating activity and burning fewer calories than anticipated,” he notes.

SEE ALSO: 7 Great Fitness Trackers

But don’t return your device just yet: “A wearable can be very motivating at showing daily successes, but you need to learn how to use the data,” says Paul Landi, an A.C.S.M. certified specialist at Professional Physical Therapy in Wilton, CT. “Use it to make small decisions that over time can add up to big improvements.”