A system (figure 1) for secluding a zone in which it is completely surrounded by a light beam barrier (14) such that any object or person striving to cross the barrier invokes an alarm if the crossing complies with various conditions The barrier is a continuous light beams formed using one light source (12) The light beam is projected from the source at one end of a path, and finally impinging on a light detector (22) The deflected light beam of the invention forms an envelope of a voluminous virtual body, that which is regarded as a seclude volume.
