Changing lifestyles have lead to public health concerns regarding chronic diseases, such as obesity and diabetes, due to poor diet and lack of physical activity. Recently, fitness trackers have become commodity and this can provide a powerful tool to help people manage their health. While research in sensors HCI has focused on individual usage, how to track physical activity and issues in adoptability, little work has explored how a larger population of users use and are influenced by trackers. In collaboration with public health officials, we are developing analytic methods to help campaign organizers understand various user tracker behaviors. This can help inform how to better engage various sub-populations and promote population health.