PROJECT SUMMARY This R34 application aims to develop and test an innovative mobile application (app) to reduce college student drinking and sexual assault risk in real time. Over 75% of campus sexual assaults involve alcohol, yet existing campus alcohol and SA prevention efforts designed for universal delivery are often siloed and limited in their ability to provide students with in-the-moment assistance to reduce risk. Smartphone apps are an integral part of college student life and are increasingly used to engage students in real-time alcohol prevention; however, none have integrated alcohol and sexual assault prevention into a single cross-cutting tool. This study addresses this gap by expanding a promising campus sexual assault prevention and response app (uSafeUS®) to include evidence-based alcohol harm reduction tools and real-time messaging to support students’ use of protective behavioral strategies (PBS) in the moments when they most need them. The uSafeUS app, currently in use on 24 US college campuses, utilizes sexual assault PBS (e.g., sharing current locations and an expected return home time with trusted peers) as the primary risk reduction mechanism for students to use in social contexts where alcohol is present, yet none of the existing features directly address alcohol consumption. This project will leverage the existing uSafeUS infrastructure and a proven user-centered development process to expand app features to include an interactive drink tracker and personalized feedback messaging to reduce alcohol consumption and increase PBS use. The expanded app (uSafeUS+) will be beta tested in an open trial to gather end-user (student) and campus administrator feedback about the app’s practical utility in the field and feasibility of the proposed implementation and evaluation plans. This will be followed by a pilot 3-arm randomized controlled trial (N = 90, 30/arm) to examine the acceptability, feasibility, and initial efficacy of uSafeUS+, relative to active (uSafeUS) and assessment-only control groups. In the short term, results from the current study will optimize the planned app and inform a fully powered multi-site hybrid effectiveness-implementation trial. Longer term, findings have the potential to inform the use of mHealth approaches for integrating prevention tools to universally deliver personalized real time prevention on college campuses where heavy drinking and sexual assault often co-occur.