Citizens provide science with a resource that is theirs—smartphones—in exchange for services that advance the community. This is especially true with earthquakes. The impact of an earthquake on people and buildings is determined not only by the earthquake's characteristics (magnitude, depth, etc.), but also by the local geology, which contributes to the phenomenon known as "site effects". High-resolution site-effect mapping in urban environments is critical for determining which areas are most vulnerable and which buildings are subjected to the most stress during a series of seismic occurrences. A study published in the journal Nature Communications by Francesco Finazzi (University of Bergamo), Fabrice Cotton (GFZ Helmholtz Centre for Geosciences, Germany), and Remy Bossu (European-Mediterranean Seismological Centre, France) represents a breakthrough: citizens' smartphones can be used to create high-resolution maps of site effects and ground shaking after an earthquake. Smartphones can measure seismic wave vibrations using built-in accelerometers, the same sensors that allow for interactive gaming. By integrating thousands of these readings with complex statistical models, researchers show that it is possible to describe how local geology amplifies seismic waves, obtaining spatial resolution considerably beyond what the national seismic network stations alone can provide. This approach is based on the Earthquake Network, a citizen science initiative founded in 2013 by Professor Francesco Finazzi. Earthquake Network turns smartphones into a global earthquake monitoring system. When an earthquake occurs, participating citizens' smartphones detect it in real time and submit data to a central server. In a matter of seconds, the population in the adjacent areas can be notified, allowing them to evacuate to safety prior to the onset of the most severe shaking.