Security system comprising light-conducting means

In a surveillance system comprising motion detection means, said motion detection means are secured by means of a security system comprising a light emitter and light-conducting which are optically coupled to said light emitter, which light-conducting means are for example provided along the circumference of a window, behind which said motion detection means are disposed. In this manner the window is secured against being damaged or against attack on its integrity, for example in the form of a film covering the window being sprayed on said window. The security system delivers an alarm signal when the intensity level is too low or too high.