A perimeter barrier system and method of monitoring a perimeter barrier are disclosed which comprise a perimeter barrier element in the form of a picket or fence panel which is mounted for limited movement by spring loading the barrier element by means of springs. An optical fiber is coupled to the barrier elements so that upon an attempt to breach the perimeter barrier system the barrier element is moved to in turn cause movement of the waveguide. A light source and detector is provided for launching light into the fiber and for detecting light which is passed through the fiber so that when the fiber is moved a parameter of the light is changed and that change in parameter is detected by detector to provide an indication of an attempt to breach the perimeter barrier system.