Abstract: To provide security against unauthorised crossing of a boundary, at least one fibre-optic wave-guide extends along the boundary. Light is directed into one end of the guide and the light leaving the guide is detected by an optical detector. An indication is given when the optical intensity of the detected light falls below a predetermined threshold, so as to warn when the wave-guide is disturbed significantly or cut through.The manufacture of a strip or strand incorporating a fibre-optic wave-guide and for use in a security system is also disclosed.

Abstract: To provide security against unauthorised crossing of a boundary, at least one fibre-optic wave-guide extends along the boundary. Light is directed into one end of the guide and the light leaving the guide is detected by an optical detector. An indication is given when the optical intensity of the detected light falls below a predetermined threshold, so as to warn when the wave-guide is disturbed significantly or cut through.The manufacture of a strip or strand incorporating a fibre-optic wave guide and for use in a security system is also disclosed.