This app was designed for participants in Understanding Society: The UK Household Longitudinal Study. As part of this study, participants aged 16 and over will be sent a Fitbit and asked to install and wear it, to collect data on their physical activity, sleep, and geolocation. The geolocation data will be collected directly from the respondent’s smartphone, if the phone and Fitbit are within Bluetooth range. If they are not in range (suggesting that the participant has gone somewhere without their smartphone), the geolocation data will be captured by the Fitbit. The purpose of this app is to retrieve all data from the Fitbit as well as the geolocation data from the phone. The Fitbit data will automatically be transferred to this app at regular intervals. In addition, participants will be asked to complete a brief daily survey within the app. This survey consists of 11 questions and takes less than 3 minutes to complete. The data collected by the app will not include any information about who the participant is. Understanding Society researchers will download the data collected by this app, process the data to derive indicators that do not identify you or your locations, and make the anonymous data available to researchers. The Understanding Society study is conducted by the Institute for Social and Economic Research at the University of Essex and funded by the Economic and Social Research Council.