UnityPhilly is a location-based app that enables a volunteer bystander who witnesses an overdose to signal for help. Other app users are alerted if they are within an estimated 15-minute radius, and asked whether they are able to respond to the scene with naloxone. The app leverages the Google Maps platform to assist responders with identifying and navigating to the location of the signaling bystander and overdose. The app also calls 911 to facilitate concurrent response by professional teams.