PROJECT SUMMARY/ABSTRACT Suicide is a leading cause of death worldwide, accounting for nearly 800,000 deaths each year.1,2 Suicide rates continue to increase in the U.S.3 Patients seen in the emergency department are at elevated risk of death4 and future suicidal behaviors.5 Most research on suicide risk factors has identified static, dispositional factors.4 For instance, distal predictors of who is at risk for suicidal behaviors include dysfunctional emotional responses1 and decision-making deficits.2 These data inform us about groups at elevated suicide risk, but do very little to predict with useful precision when people will have suicidal thoughts or act on suicide thoughts. Thus, there is an urgent need to identify proximal risk factors for suicide risk. The Parent Study, “EMERGE: Ecological Momentary Evaluation of Responses to Gain/Loss and Emotions” (R01MH128546), addresses this question with ecological momentary assessment (EMA) of emotions and reinforcement learning as predictors of near-term suicidal thoughts and behaviors in 170 emergency department patients seen for a suicide-related complaint. Yet emergency department patients are disproportionately low income7 and minoritized,8 and many are unstably housed.9 This population is therefore simultaneously critical to consider in suicide research and difficult to retain in research studies, as evidenced by high attrition from enrollment to our initial assessment period. This supplement application is intended to address these challenges that have the potential to compromise our efforts to (1) collect adequate data to allow for an examination of our primary aims with sufficient power, (2) manage risk without undermining data validity, and (3) understand barriers to implementing future clinical interventions based on our results. Specifically, Aim 1 increases the sample size of enrolled participants to overenroll to 210 and increase monetary incentives to allow for adequately powered analyses. Aim 2 evaluates participants’ experiences of the risk assessment protocols and their impact on data validity via additional survey and interview methods. Aim 3 identifies barriers and facilitators of accessing psychiatric care in this population via additional survey and interview methods. To date, our research team has shown the ability to enroll participants on target and conduct this study safely. This supplement will leverage this study of a particularly vulnerable population and allow us to make substantial inroads in improving our suicide research and care.