Method of detecting break-ins in an intrusion-detection barrier which comprises an array of sensors in signal communication with one another and connected to a control unit , said method comprising the steps of: - calibrating at least one sensor of the array ; - detecting an external forcing applied to the intrusion-detection barrier , said external forcing having oscillation forcing frequencies; - generating an alarm signal when said external forcing is detected; characterized in that - the step of calibrating at least one sensor comprises the sub-steps of: - applying mechanical stress to said intrusion-detection barrier to cause said intrusion-detection barrier to resonate at its characteristic frequencies; - creating a digital filter for said sensor configured to identify said characteristic frequencies; - the step of detecting an external forcing applied to the intrusion-detection barrier comprises the sub-steps of: - applying said filter to identify the forcing frequencies applied to the intrusion-detection barrier , and discriminating said forcing frequencies from the characteristic frequencies of the intrusion-detection barrier , - selecting at least one energy threshold value, - calculating an energy value for each of said forcing frequencies, - comparing each energy value with the energy threshold value, - the step of generating said alarm signal comprises the sub-step of generating the alarm signal when at least one energy value is greater than the energy threshold value. - calibrating at least one sensor of the array ; - detecting an external forcing applied to the intrusion-detection barrier , said external forcing having oscillation forcing frequencies; - generating an alarm signal when said external forcing is detected; characterized in that - the step of calibrating at least one sensor comprises the sub-steps of: - applying mechanical stress to said intrusion-detection barrier to cause said intrusion-detection barrier to resonate at its characteristic frequencies; - creating a digital filter for said sensor configured to identify said characteristic frequencies; - applying mechanical stress to said intrusion-detection barrier to cause said intrusion-detection barrier to resonate at its characteristic frequencies; - creating a digital filter for said sensor configured to identify said characteristic frequencies; - the step of detecting an external forcing applied to the intrusion-detection barrier comprises the sub-steps of: - applying said filter to identify the forcing frequencies applied to the intrusion-detection barrier , and discriminating said forcing frequencies from the characteristic frequencies of the intrusion-detection barrier , - selecting at least one energy threshold value, - calculating an energy value for each of said forcing frequencies, - comparing each energy value with the energy threshold value, - applying said filter to identify the forcing frequencies applied to the intrusion-detection barrier , and discriminating said forcing frequencies from the characteristic frequencies of the intrusion-detection barrier , - selecting at least one energy threshold value, - calculating an energy value for each of said forcing frequencies, - comparing each energy value with the energy threshold value, - the step of generating said alarm signal comprises the sub-step of generating the alarm signal when at least one energy value is greater than the energy threshold value. <EOS>