Part 1a: Testing and Initial Deployment of sensors in target populations: We will use unit testing to extensively test our mobile software suite. We will recreate several usage scenarios and environmental conditions that our deployment test bed is likely to encounter. A total of 50 Hispanic and African American youth will be recruited to assist in technology development: 1) an advisory group of 10 youth, 2) 20 youth to participate in laboratory testing of the biomonitors and 3) 20 youth to wear the biomonitors and provide data and feedback. The advisory group of 5 African American and 5 Hispanic youth will be retained throughout the developmental phase to periodically visit our laboratory and test-run the sensors (50% female, 12-17 years of age). We will recruit a separate group of 10 African American and 10 Hispanic youth (50% female, 12-17 years of age) to participate in idea building sessions to ensure that sensors will be attractive and wearable, and to test the ease of usability of our mobile software suite. The initial deployment phase includes training the children on how to wear and remove the sensors. In order to minimize errors in configuring the software, we envision that our mobile software will have several in-built checks to advise the user if any of the sensor readings do not match expected sensor behavior, and suggest simple solutions to properly configure the sensors. In addition to providing the wearable sensors we will also provide each child with a mobile phone platform which interfaces with these sensors. Since the mobile device has to transmit the data to the back-end servers, we will opportunistically use an open WiFi network that a phone can connect to transfer data both efficiently and economically. In the absence of WiFi networks the mobile software will automatically use the cellular data network to transmit the data. For using cellular data network we plan to explore several available options that allow users to send unlimited data for less than 10$ a month in the Los Angeles area from their mobile phones. For laboratory testing of sensors, 10 Hispanic and 10 African American youth will spend 3-6 hours wearing the sensors and following protocols for walking, sitting, standing and doing various daily activities either at Dr. Spruijt-Metz's Physical Activity Observation Laboratory at USC HSA, or to the Motion Capture Laboratory at the Viterbi School of Engineering on USC Main Campus. Once the software and hardware is determined to be robust enough for deployment we will conduct our initial monitoring study with 10 African American and 10 Hispanic youth (50% female, 12-17 years of age). Children will wear the devices for three periods of one week (7 days), after which they will participate in brief individual interviews and surveys to ascertain ease of wear and to find ways to motivate and incentivize teens for wearing the sensors. Data collected from these weeks of wear will be used for the remaining data analysis and web presentation phases of the study.