Wearing a fitness tracker may help you keep tabs on how many steps you take, but the devices themselves — even with the lure of a cash reward — probably won't improve your health.

Wearing a fitness tracker to help you lose weight? Simply counting the steps you’ve taken and how many calories you’ve burned will get you nowhere when it comes to weight loss, a new study is warning.

It was a very merry Christmas for fitness-tracking device maker Fitbit.