PROJECT SUMMARY/ABSTRACT Binge drinking (BD) is defined as a rapid consumption of alcohol that brings blood alcohol content to .08% or higher, typically described as ≥4 drinks for women and ≥5 drinks for men per occasion. BD is associated with many adverse consequences, including accidents, physical and sexual assault, and alcohol poisoning, as well as increased risk for developing an alcohol use disorder (AUD). BD is highly prevalent among American college students, with past-month estimates of 30% or greater. College – in particular the first six weeks – represents a critical time for the onset and development of harmful alcohol use. Drinking patterns established early in college influence alcohol use in the years following, underscoring the need for research into the early detection and prevention of BD in first-year college students. Certain health behaviors – namely sleep and physical activity – have been shown to bidirectionally influence BD, though the direction of the relationship is equivocal in college students. Furthermore, both acute and recurrent BD have been associated with psychophysiological changes, including diminished heart rate variability (HRV), leading some researchers to conceptualize HRV as a biomarker of AUD. However, existing research is either correlational or describes the impact of drinking on HRV, rather than examining HRV as a risk factor for BD, despite conceptual support for this direction. Moreover, measuring health behaviors and psychophysiology with traditional self-report measures or laboratory paradigms poses methodological challenges such as biases in participant recall, high participant burden, low compliance, and limited ecological validity. In contrast, smartwatches – which can passively sense many health variables with minimal user input – are being increasingly employed in psychological and medical research as a way of mitigating these concerns. The proposed study will utilize passive sensing via smartwatches in a sample of 100 incoming college freshmen (two cohorts of 50) without a history of BD or AUD prior to the start of their first semester. Participants will complete a baseline assessment of their substance use history followed by a six-week smartwatch monitoring period. Throughout the semester, participants will complete weekly self-report measures of BD accompanied by periodic timeline follow-back interviews and urine ethyl glucuronide screening for validation purposes. Follow-up assessments will be completed at the end of the first semester (4 months) and second semester (9 months). Specific variables of interest are: physical activity (steps and logged workouts); sleep (duration, chronotype, and social jetlag); and HRV. Data collected during the smartwatch monitoring period will be examined as prospective predictors of BD onset and frequency, with an exploratory aim focusing on AUD onset. Results from this study will help identify novel biopsychosocial risk factors for BD during a critical per...