RecruitingClinical trialUnityPhilly Response App for Overdose ReversalThe goal of this clinical trial is to discover if an overdose prevention app (UnityPhilly) can encourage citizen responders to respond and prevent opioid overdoses using the UnityPhilly app. The main hypotheses to answer are: Hypothesis 1: UnityPhilly signal rates relative to EMS calls will increase over time. The primary outcome will be assessed as the total number of overdoses signaled by participants relative to all overdose-related EMS calls, per year. Hypothesis 2: The number of cases where a nearby UnityPhilly participant successfully reverses an overdose with naloxone will increase over time. The primary outcome will be assessed as the number of successful reversals relative to the total number of responder arrivals, per year. Participants will be supplied with the UnityPhilly app, training on how to use the app and respond to an opioid overdose using naloxone, and respond to follow up surveys about their experiences.