PhysiAware is an app designed to collect data from physiological sensors (heart rate, galvanic skin response, motion) worn by participants, as well as responses to short surveys of participants and their GPS location during research studies. Data collected by the app are transmitted to a secure research server for subsequent analysis and deleted from the smartphone. The use of this app in research is subject to Institutional Review Board (IRB) approval and is available only to participants that have been enrolled in an IRB-approved research study and have gone through the process of informed consent. This app is not available for public use outside of a research study context. In order to use the app, an enrolled participant will need to enter a code issued by the research study during the enrollment process. This GPS location information collected by this app together with physiological sensor data will be used to detect and predict situations when study participants are likely to engage in certain types of recurring behavior (e.g., smoking a cigarette or using other tobacco products).