A safety capsule for containers, comprising: an external cap which has at least a top part that is transparent and/or the conformation of which consists of a polarized or non-polarized lens or set of lenses, wherein the top part of the external cap comprises a plurality of lenses of prismatic shape; an internal element, located inside the external cap and configured to be associated, in a removable manner, with an opening of a container; a coupling means configured to couple the external cap or the internal element to the neck of the container; connecting means (4, 5), interposed between the external cap and the internal element, structured so as to leave the external cap and the internal element unconstrained with respect to a movement for opening or removal of the external cap between a closed position and an intermediate position, and solidly constrain the external cap and the internal element with respect to the movement for opening or removal of the external cap between the intermediate position and an opening position; a signalling means, structured to take on a given configuration in the intermediate position; characterized in that: the top part of the external cap comprises a first plurality of lenses of prismatic shape, located parallel to a main direction, and a second plurality of lenses, of prismatic shape, located parallel to an auxiliary direction, which is inclined relative to the main direction; wherein the first plurality of lenses is located on one side of the top part and the second plurality of lenses is located on the opposite side of the top part; wherein the top part comprises at least a transparent portion which is not occupied by the first plurality of lenses and the second plurality of lenses. an external cap which has at least a top part that is transparent and/or the conformation of which consists of a polarized or non-polarized lens or set of lenses, wherein the top part of the external cap comprises a plurality of lenses of prismatic shape; an internal element, located inside the external cap and configured to be associated, in a removable manner, with an opening of a container; a coupling means configured to couple the external cap or the internal element to the neck of the container; connecting means (4, 5), interposed between the external cap and the internal element, structured so as to leave the external cap and the internal element unconstrained with respect to a movement for opening or removal of the external cap between a closed position and an intermediate position, and solidly constrain the external cap and the internal element with respect to the movement for opening or removal of the external cap between the intermediate position and an opening position; a signalling means, structured to take on a given configuration in the intermediate position; characterized in that: the top part of the external cap comprises a first plurality of lenses of prismatic shape, located parallel to a main direction, and a second plurality of lenses, of prismatic shape, located parallel to an auxiliary direction, which is inclined relative to the main direction; wherein the first plurality of lenses is located on one side of the top part and the second plurality of lenses is located on the opposite side of the top part; wherein the top part comprises at least a transparent portion which is not occupied by the first plurality of lenses and the second plurality of lenses. the top part of the external cap comprises a first plurality of lenses of prismatic shape, located parallel to a main direction, and a second plurality of lenses, of prismatic shape, located parallel to an auxiliary direction, which is inclined relative to the main direction; wherein the first plurality of lenses is located on one side of the top part and the second plurality of lenses is located on the opposite side of the top part; wherein the top part comprises at least a transparent portion which is not occupied by the first plurality of lenses and the second plurality of lenses.