The use of mobile sensing systems (MSS), via smartphone, in various application domains such as (medical and healthcare) are growing rapidly. However, there is a very limited research and development effort put toward exploiting these smartphone sensing technologies to promote human beings wellness and active lifestyle. This paper introduces “Alert Me”, a smartphone application that quantifies the sedentary behavior (e.g., prolonged sitting) and aims at reducing it. It generates the timely personalized messages by suggesting short breaks to promote active lifestyle. We utilize the accelerometer sensor of smartphone to observe the sedentary behavior of the user under free-living conditions. Alert Me computes the features over accelerometer data and performs the classification to generate the alerts by using computation power of smartphone. It facilitates the users to create a personal profile and manage alerts according to their own choice. We develop an initial working prototype to evaluate the applicability of our approach in a real-world scenario to avoid prolonged uninterrupted periods of sedentary time.