Think you have to wear a dedicated fitness tracker to get accurate data? Don't worry -- you may have a good excuse to skip the wristband. The University of Pennsylvania has published a study showing that smartphone apps' step counts are reasonably on the mark, at less than a 7 percent variance between their data and what observers saw first-hand. With wearables, it's all over the map. Some are very accurate, like Fitbit's One and Zip; others don't give you much of an advantage over a phone, and Nike's Fuelband was sometimes off by a wide margin.