A security system lays out a sensing optical fiber tautly at the perimeter of an area to be secured. The sensing optical fiber has at least one sensing Fiber Bragg Grating (FBG) which is stretched when the sensing optical fiber is stretched by an intruder. The center wavelength of reflection of the stretched sensing FBG shifts towards longer wavelengths. The shifted center wavelength of reflection is detected using a reference FBG with a longer center wavelength of reflection. The sensing optical fiber has a loose buffer coating for isolating the sensing optical fiber and the sensing FBG from nuisance disturbances and noise such as vibrations caused by wind. Trip wires may be attached to the sensing optical fiber for enhancing intruder detection. A cut of the sensing optical fiber may be detected by monitoring the optical power exiting the far end of the sensing optical fiber.