Selecting volunteer community first responders based on how quickly they can reach a cardiac arrest scene, rather than simply how close they are, significantly increases the likelihood that a trained volunteer will arrive before emergency medical services (EMS), according to late-breaking research presented at the American Heart Association's Resuscitation Science Symposium 2026 in Chicago.
The ALARM randomized clinical trial, conducted by researchers in Freiburg, Germany, compared three strategies for alerting trained volunteers through a smartphone app. One strategy alerted volunteers within a small geographic circle of about 600 meters, another within a larger circle of about 2,500 meters, and a third used a “smart alerting” calculation that considered expected travel time to the patient compared with ambulance arrival. Over seven months in 2024, the system randomly switched strategies daily, with neither dispatchers nor volunteers aware of which was active.
Results showed that a trained volunteer arrived before the ambulance in only 31% of emergencies when alerts went to the small geographic circle. That figure rose to 57% with the larger circle and 58% with smart alerting. Moreover, both the large-circle and smart strategies more often resulted in more than one volunteer arriving, which is important because CPR is physically demanding and allows rescuers to take turns.
“Our study results indicate that how these trained volunteers are chosen and assigned to cardiac emergencies really matters,” said Michael Mueller, M.D., senior study author and chair of the department of anesthesiology, intensive care and emergency medicine at St. Josef's Hospital in Freiburg. “When the app evaluated who can actually get there fastest, instead of just who is closest on a map, more than half of patients had a trained volunteer providing care before the ambulance arrived.”
Smart alerting also proved more efficient: 31% of volunteers who accepted an alert were deliberately not sent because calculations showed they would likely arrive after EMS. Only 69% of volunteers received a task under smart alerting, compared with 90% for the small circle and 94% for the large circle, yet it achieved nearly the same high arrival rate as the large-circle approach.
The findings matter because every minute without CPR lowers survival chances for out-of-hospital cardiac arrest. The American Heart Association's 2025 Emergency Cardiovascular Care Guidelines note that prompt CPR or defibrillation greatly improves survival, with immediate CPR linked to two to three times higher survival rates. Small, fixed geographic radii are still widely used internationally, Mueller said, suggesting such systems may be “leaving many potential lifesavers untapped.”
The study measured response times, not patient survival. “Whether smart alerting improves survival odds needs to be examined in future research,” Mueller said. The trial was simultaneously published in the Journal of the American Heart Association. For more information on cardiac arrest response, see the AHA's Treatment of Cardiac Arrest resources and its Join the Nation of Lifesavers by learning CPR today initiative. Additional details are available via the Link to abstract and the symposium's Online Program Planner.
