Surveillance systems that automatically detect illegal behaviors performed by unaware people have a wide range of applications: security, healthcare, conservation of cultural heritage and so on. In particular monitoring public areas such as museums and archaeological sites is a challenging problem that has to be solved in order to avoid irreparable damages to historical heritage. In this paper a system able to check by common digital RGB cameras unexpected accesses to forbidden areas in a public museum is presented. The reliability of the proposed framework is shown by large experimental tests performed in the Messapic Museum of Egnathia (Italy) .