The purpose of the proposed study is to test the efficacy of individual components of a smartphone application designed using theories of human behavior to promote physical activity in low-active adults. Smartphones have become commonplace: approximately two-thirds of adults own a smartphone. They allow for wireless internet connectivity and the ability to communicate via voice and text message at any time. Perhaps most importantly from the perspective of behavior change, the devices are often carried on the person at all times. In recent years researchers have attempted to use these devices to promote physical activity, but continue to encounter a number of barriers. Notably, development in the commercial sector far outpaces the standard randomized controlled trial (RCT) cycle. As a result, researchers utilizing RCT designs find it difficult to publish findings that are relevant to current technology. Additionally, this approach typically examines a full application that includes a package of features, making it difficult to draw conclusions about single intervention components. This has resulted in a commercial sector that produces a large number of physical activity applications that are not evidence based. The present study uses a factorial design to study the individual and combined efficacy of two theory-based modules: A guided goal-setting module, and a points-based feedback system. If successful, the results of this study will help to guide a fast-moving commercial sector toward the development evidence-based applications, which has the potential to yield a large public health impact.