  Counting the number of people is something many security application focus
on, when dealing with controlling accesses in restricted areas, as it occurs
with banks, airports, railway stations and governmental offices. This paper
presents an automated solution for detecting the presence of more than one
person into interlocked doors adopted in many accesses. In most cases,
interlocked doors are small areas where other pieces of information and sensors
are placed in order to detect the presence of guns, explosive, etc. The general
goals and the required environmental condition, allowed us to implement a
detection system at lower costs and complexity, with respect to other existing
techniques. The system consists of a fixed array of microwave transceiver
modules, whose received signals are processed to collect information related to
a sort of volume occupied in the interlocked door cabin. The proposed solution
has been statistically validated by using statistical analysis. The whole
solution has been also implemented to be used in a real time environment and
thus validated against real experimental measures.
