PROJECT SUMMARY The proposed study aims to reduce firearm-related deaths in children by scaling out an evidence-based secure firearm storage intervention. The rate of firearm-related deaths increased by 41% from 2018-2021 across all intents, and firearms are now the leading cause of death for youth ages 1-19. Secure firearm storage is a health behavior that is critical for reducing unauthorized access to firearms and the risk of suicide, homicide, and unintentional injuries. S.A.F.E. Firearm is an evidence-based intervention that includes (1) brief, parent-directed discussion on secure firearm storage using a motivational interviewing and harm reduction approach and (2) free cable locks offers to all parents during well child visits in pediatric primary care. Importantly, S.A.F.E. Firearm has potential to save lives beyond primary care, and pediatric inpatient settings are an advantageous context for S.A.F.E. Firearm implementation. Across the U.S. there are over 250 children's hospitals, approximately two million children are hospitalized yearly, and parental engagement is a core feature of care. Moreover, hospitals are essential settings for children disadvantaged by structural determinants and inadequate access to outpatient services. Children's Hospital of Philadelphia (CHOP) is a large, nonprofit pediatric health care system with two freestanding children's hospitals in the greater Philadelphia region. Our team has pilot tested firearm safety initiatives in the emergency department, select primary care sites, and the pediatric intensive care unit. Through our formative work, we have identified bedside nurses as vital potential implementers. In Aim 1 of this proposal, we will adapt S.A.F.E. Firearm for the pediatric inpatient setting and nurse-led delivery using intervention mapping. Anticipated products are an adapted intervention and optimized bundle of implementation strategies. In Aim 2 we will conduct a parallel cluster randomized hybrid Type 2 effectiveness-implementation trial across two CHOP hospitals. Twelve inpatient nursing units will be randomized to receive adapted S.A.F.E. Firearm or usual care, defined as routine clinical care plus free cable locks available in the hospital safety center. We will test whether parents exposed to adapted S.A.F.E. Firearm report greater improvements in secure storage (primary outcome) compared to parents exposed to usual care over one year of active implementation. Secondary outcomes are additional firearm safety behaviors (e.g., firearm removal). We anticipate 14,400 eligible patient visits across the 12 units. Guided by the RE-AIM framework with equity considerations, we will examine the effect of the implementation strategy bundle on S.A.F.E. Firearm outcomes in Aim 3. Our primary implementation outcome is reach (i.e., electronic health record-documented program delivery). Secondary outcomes include fidelity, acceptability, and maintenance. We will explore implementation strategy mechanisms via...