Abstract: An anti-intrusion device for fences or the like, comprising at least one, preferably two or more cables (3), each one composed of at least one or a bundle of optical fibres (103) and of an outer protection sheath (203), which optical fibre cables (3) are subtended in a substantially longitudinal direction of a section or a perimeter to be protected and are supported or holded each one at a different height at a plurality of supporting points spaced apart arranged and wherein, at least at some of said supporting points, first means (8, 9) deforming and/or blocking each optical fibre cable (3) are provided, which first deforming and/or blocking means (8, 9) may be moved from a rest position in which they do not interfere with the optical fibre cable (3) to an active position deforming and/or blocking the optical fibre cable (3) in which an optical signal transmitted through the optical fibre cable (3) is attenuated under a predetermined threshold value or it is anyway modified, and which first deforming and/or