SECURITY SYSTEM

PROBLEM TO BE SOLVED: To install a facility not to generate any dead angle at low cost by providing a transmission antenna for transmitting radio waves at a specified central frequency and a reception antenna, to which a waveform analytic means is connected, around a security object zone. SOLUTION: A transmission antenna 10 and a reception antenna 20 are housed inside a wall 2 of a room 1 and connected to a transmitter and a receiver inside a control room. This transmitter always transmits the radio waves of narrow band higher than a central frequency 1GHz from the transmission antenna 10 to a security object zone A. On the other hand, a spectrum analyzer for monitoring the waveforms of received radio waves is connected to the receiver connected with the reception antenna 20, and the analyzed received waveforms are monitored. At such a time, when the frequency spectrum waveform of any peculiar received radio wave is set as normal one concerning the object zone A and there is an invader in the object zone A, the frequency spectrum waveform of narrow band of the received radio wave is changed through the analyzer so that the invader can be detected.