Smart cities are trying to improve energy efficiency by reducing energy consumption and increasing energy production, for example with solar systems on public buildings. Also the use of digitization and information technology helps to control the functions of cities more efficiently. Various sensors are distributed throughout the city and can be used for a wide variety of applications. For example buses in Belgrade and Pancevo are equipped with sensors that measure air quality. In some US cities sensors measure the fillinig level of public garbage cans: only full garbage cans are targeted and emptied.