In recent years, our cities have become increasingly smart, thanks to the massive use of IoT (Internet-of-Things) sensors and smart devices owned by people, life in the city has improved considerably. One of the most popular and important studies concerns the monitoring of people flows with the aim to guarantee both better services to citizens, from the point of view of dimensioning transportation networks, bike lanes, and public routes. However, it is also significant for identifying and quantifying people in sensitive areas (e.g., for safety and security purposes, such as during large crowd gatherings) or in areas of transit. It is essential to introduce new technologies for tracking people in case of health emergencies, such as the one we have been experiencing for many months.