The invention relates to a security sensor (10) comprising a sensing device (21), a coming optical fiber element and a going optical fiber element, the sensing device (21) comprising a housing that receives a first end of the coming element and a first end of the going element. It is characterized in that the first end of the coming element and the first end of the going element in the housing are not aligned, and in that when a light beam enters the housing through the first end of the coming element, at least part of said light beam is reflected within the housing and exits through the first end of the going element.