Safety method for authorizing an operation, wherein the operation comprises: unlocking a cell phone, a smartphone, or another electronic device, performing an operation by the same or by an application installed in the same, said method comprising: - providing: - a safety device comprising: - a supporting structure; - a color-shift structure coupled to the supporting structure on a side or a face of this latter; - a first safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the first safety string and color-shift structure are overlapped on each other; - a second safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the second safety string and the color-shift structure are not overlapped on each other; - a light source; - an optical reader capable of acknowledging the first and second safety strings of the safety device; - lighting, by the light source, the color-shift structure of the safety device and performing, by the optical reader, a first reading of the first and second safety strings by holding a predefined relative first position and first orientation among the safety device, the light source, and optical reader; - lighting, by the light source, the color-shift structure of the safety device and performing, by the optical reader, a second reading of the first and second safety strings by holding a predefined relative second position and second orientation among the safety device, the light source, and optical reader; - authorizing the operation if: 1) in the first reading, both the first and second safety strings are visible and acknowledged by the optical reader; 2) in the second reading, only the second safety string is visible and acknowledged by the optical reader, and the first safety string is invisible to the optical reader. - providing: - a safety device comprising: - a supporting structure; - a color-shift structure coupled to the supporting structure on a side or a face of this latter; - a first safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the first safety string and color-shift structure are overlapped on each other; - a second safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the second safety string and the color-shift structure are not overlapped on each other; - a light source; - an optical reader capable of acknowledging the first and second safety strings of the safety device; - a safety device comprising: - a supporting structure; - a color-shift structure coupled to the supporting structure on a side or a face of this latter; - a first safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the first safety string and color-shift structure are overlapped on each other; - a second safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the second safety string and the color-shift structure are not overlapped on each other; - a supporting structure; - a color-shift structure coupled to the supporting structure on a side or a face of this latter; - a first safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the first safety string and color-shift structure are overlapped on each other; - a second safety string made in the supporting structure and arranged on said side or face of the supporting structure so that the second safety string and the color-shift structure are not overlapped on each other; - a light source; - an optical reader capable of acknowledging the first and second safety strings of the safety device; - lighting, by the light source, the color-shift structure of the safety device and performing, by the optical reader, a first reading of the first and second safety strings by holding a predefined relative first position and first orientation among the safety device, the light source, and optical reader; - lighting, by the light source, the color-shift structure of the safety device and performing, by the optical reader, a second reading of the first and second safety strings by holding a predefined relative second position and second orientation among the safety device, the light source, and optical reader; - authorizing the operation if: 1) in the first reading, both the first and second safety strings are visible and acknowledged by the optical reader; 2) in the second reading, only the second safety string is visible and acknowledged by the optical reader, and the first safety string is invisible to the optical reader. 1) in the first reading, both the first and second safety strings are visible and acknowledged by the optical reader; 2) in the second reading, only the second safety string is visible and acknowledged by the optical reader, and the first safety string is invisible to the optical reader.