Fastened to a tyre is a detecting device consisting of a detecting unit including an antenna operatively connected to a sensor unit and a power supply unit including a piezoelectric element mounted in a housing. The piezoelectric element is disposed within the housing so as to have a first end substantially fixed to the housing and a second end associated with a loading mass, a gap being formed between at least one inner wall of the housing and an outer surface of the loading mass. The piezoelectric element is positioned substantially along a plane orthogonal to a radial direction of the tyre. An anchoring body has a base portion with a fastening surface secured to the radially internal surface of the tyre. The detecting unit is brought into engagement with the anchoring body by insertion of the inner perimetral edge of the antenna into a perimetral groove formed between the base portion and a retaining portion.