For operators of shopping centers, airports, trade fairs, railway stations etc. it is interesting to know how many visitors stay at a certain place at a certain time and how they move. This way, it is possible to display on a heat map, which places are most frequented – which can be useful for the security staff and others. An alarm can be given when a predefined amount of people stays at a point in the building. After that, actions can be triggered, for example an unscheduled cleaning or a redirection of itineraries. For the marketing department it is interesting to know such numbers. They can also be used to direct people to certain shops or advertising spaces. Organizers of trade fairs profit from the technology as they get some precise visitor numbers when negotiating with exhibitors. The installation is made client-based or server-based.