INTRODUCTION: We developed a new smartphone application to deliver an automated external defibrillator (AED) to out-of-hospital cardiac arrest scene. The aim of this study was to evaluate whether an AED could be delivered earlier with or without an application in a simulated randomized controlled trial. METHODS: Participants, who were asked to work as bystanders, were randomly assigned to either an application group or control group and were asked to bring an AED in both groups. The bystanders in the application group sent a signal notification using the application to two responders, who were stationed within 200 meters of the arrest scene, to carry an AED. The primary outcome was the AED delivery time by either the bystander or his/her responder. RESULTS: In total, 61 bystanders were eligible and randomized to either the application group (32) or the control group (29). The 52 with time data were available and analyzed. The AED delivery time by either the bystander or his/her responder was significantly shorter in the application group than in the control group [133.6 (44.4) seconds vs. 202.2 (122.2) seconds, P = 0.01]. CONCLUSIONS: In this simulation-based trial, AED delivery time was shortened by our newly developed smartphone application for the bystander to ask nearby responders to find and bring an AED to the cardiac arrest scene (UMIN-Clinical Trials Registry 000016506).