Secure storage of firearms is a critical strategy to prevent suicide, unintentional injury, intimate partner homicide, and gun theft. Forty percent of American households own at least one firearm, and the majority store at least one firearm unlocked. Health systems can promote secure storage through counseling and education, and efforts are most successful when they include distribution of a no-cost secure locking device. Most secure storage programs distribute cable locks, which are inexpensive and convenient for distribution. However, the most common reason for firearm ownership in the U.S. is protection from other people, and firearm owners who value protection also prioritize speed and ease of access to their firearm during a potential emergency. Firearm owners with these priorities are less likely to store their firearms securely, and when offered a choice, prefer to use a lock box over a cable lock. To date, no randomized trials have tested the comparative effectiveness of distributing cable locks vs. providing the firearm owner’s preferred device. Furthermore, little research exists on the effectiveness of secure storage promotion among the range firearm owners, which is especially important as firearm ownership has risen among many demographic groups. This proposal aims to address these gaps in the literature through a hybrid type 1 effectiveness-implementation trial with these specific aims: 1) Compare the effectiveness of distributing cable lock(s) (usual practice) vs. a choice of a lock box and/or cable locks (choice of preferred devices) on participants’ self-reported firearm storage practices; (2) Compare program uptake and storage outcomes across participant demographic, neighborhood socioeconomic, and behavioral and firearm ownership characteristics; and 3) Measure feasibility, acceptability, and appropriateness and identify barriers and facilitators to implementing and scaling the interventions in the study arm among community health sites participating in the trial. The findings will provide insights into factors associated with successful program engagement and secure storage practices and will guide the design and tailoring of future interventions to optimize effectiveness and improve health for all. This study will provide health system and community health stakeholders and policy makers crucial evidence to inform the adoption of secure storage promotion strategies in a range of contexts with high potential for reducing firearm injury morbidity and mortality.