question: Goal: The purpose of this article is to introduce a new strategy to identify areas with high human density and mobility, which are at risk for spreading COVID-19 Crowded regions with actively moving people (called at-risk regions) are susceptible to spreading the disease, especially if they contain asymptomatic infected people together with healthy people Methods: Our scheme identifies at-risk regions using existing cellular network functionalities— handover and cell (re)selection—used to maintain seamless coverage for mobile end-user equipment (UE) The frequency of handover and cell (re)selection events is highly reflective of the density of mobile people in the area because virtually everyone carries UEs Results: These measurements, which are accumulated over very many UEs, allow us to identify the at-risk regions without compromising the privacy and anonymity of individuals Conclusions: The inferred at-risk regions can then be subjected to further monitoring and risk mitigation