With around 44,000 participants and more than 350,000 to 400,000 spectators along the running course, the Vienna City Marathon is one of the largest mass sporting events in the world. For four years now, smartphone app-based security solutions for spectators, developed at the Institute for Pervasive Computing at Johannes Kepler University Linz, have been in use. At yesterday's 32nd edition of Europe's second-largest sporting event, 19,340 app users kept themselves continuously informed about what was happening on the running course, while at the same time contributing to an early warning system for dangerous situations due to unpredictable crowd behavior.