The cable is installed underground along the prison perimeter. When someone or machinery invades the protected area, the vibration sensing fiber optic cable buried underground will convert the tiny vibration caused by human or mechanical intrusion into optical signal and transmit it to acquisition device which transmits the optical signal to alarm host after analysis and processing it. The sensor used is of potential-free distribution type. Its wiring is simple, convenient and flexible. It has strong adaptability to all kinds of harsh natural environments and high-temperature and low-temperature environments. It is well received by users.