A monitoring device for tyres for vehicle wheels comprising: an electronic unit (20); a connecting member (30) configured for constraining said electronic unit (20) to a tyre (1 ), said connecting member (30) comprising: a first and a second base portion (31, 32), mutually separated by a separated region (33), each of said base portions (31, 32) having a respective base surface (31 a, 32a) associable with an inner surface (2) of a tyre (1 ); a housing portion (34) associated with said base portions (31, 32) defining, in cooperation with said base portions (31, 32), a cavity (35) for housing said electronic unit (20),wherein said housing portion (34) comprises at least one side structure (34a), configured for exerting a containing action at least relative to movements of said electronic unit (20) carried out in a major extension direction (X) of said separation region (33) and with respect to movements of said electronic unit (20) carried out in a direction orthogonal to the major extension direction (X) of said separation region (33) wherein said cavity (35) is confined at least by a side surface (351 ) defined by an inner surface (340) of said side structure (34), wherein said electronic unit (20) comprises at least one sensor (21 ), at least one antenna (22) and a holding body (26); for housing at least said sensor (21 ) and said antenna (22), wherein said holding body (26) has at least one side surface (261 ), wherein, when said electronic unit (20) is inserted in said cavity (35): the side surface (261 ) of the holding body (26) faces the side surface (351 ) of the cavity (35), and the sizes of said cavity (35) and of said holding body (26) are such as to form at least one first gap (100) at least partly separating the side surface (261) of the holding body (26) and the side surface (351) of the cavity (35). Also described are a tyre (1 ) provided with said monitoring device (10) and a method for installing an electronic unit (20) in a tyre (1 ).