Recent studies demonstrated that the duration of inactivity (sedentary state) is independently associated with increased risk of cardiovascular disease. Our goal was to develop the technology that can measure the amount of inactivity in real time, remind a person that a preprogrammed period of inactivity has occurred and encourage a period of activity, and provide web-based feedback with tailored information to the participant and investigators. Once it was developed, we carried out a pilot study in a group of sedentary overweight women. The objective of the study was to assess potential of the mobile app to reduce inactivity in our target population. A randomized crossover design was employed with study subjects randomly assigned to a 4-week each 'message-on' and 'message-off' periods. Out of 30 enrolled subjects, 27 completed the study. The average age of particpants was 52±12; BMI: 37±6; 47% were white and 47% were African American. Overall, inactivity was significantly lower (p<0.02) during 'message-on' periods (24.6%) as compared to the 'message-off' periods (30.4%). We conluded that mobile app monitoring inactivity and providing a real-time notification when inactivity period exceeds healthy limits was able to significantly reduce inactivity periods in overweight sedentary women.