Free mContain app for Greater Memphis area also provides crowding alerts for physical distancing. 

Researchers at the University of Memphis-based Center of Excellence for Mobile Sensor Data-to-Knowledge (MD2K) have introduced a new mobile app that may support physical distancing during the COVID-19 pandemic. MD2K is supported by NIH with a grant administered by the National Institute for Biomedical Imaging and Bioengineering (NIBIB).