In this paper we suggest a wireless embedded system for estimating the closeness and the interaction time between mobile and fixed units for personal safety applications. In particular, the system provides a technological support during emergency or critical situations - where personnel has to safety move in a critical dynamic scenario - by automatically delimiting a dangerous area previously characterised by a third party. The suggested approach significantly extends existing solutions not requiring any absolute position information or a fixed infrastructure. Moreover, being deeply embedded, it can be quickly deployed in a new environment