The present invention relates to a device (10) for controlling the unwinding of an actuation cable (2) of an airbag, comprising a main body (3) inside which a movable element (6) and a locking system of the movable element (6) are housed. The movable element (6) is rotatably arranged in said main body (3) and comprises winding devices, arranged on a first surface of the movable element (6), and configured to wind and unwind the actuation cable (2). The movable element (6) also comprises a retaining device (7) arranged on a second surface of the movable element (6) and configured to hold an end of the actuation cable (2). The locking system of the movable element (6) comprises a crown element (11), integral with the main body (3), and having a profile provided with a plurality of recesses (12) facing a second surface of the movable element (6), said second surface being arranged at one end of the movable element opposite the first surface. The locking system further comprises a blocking assembly, arranged on said second surface of the movable element (6), which comprises a helical spring (13) which works both in compression and upon reaching Euler's buckling load and which has at least one central portion free from constraints. The blocking assembly further comprises a shaped element (14) hinged to the movable element (6), which has an engagement section (15), adapted to engage said recesses (12), and a housing seat (17) in which a first end of the helical spring (13) is constrained; the housing seat (17) is arranged such that, when the cable is at rest, the thrust of the spring on the seat (17) maintains the engagement section (15) distant from said recesses (12). The blocking assembly further provides a matching element (18) in which a second end of the helical spring (13) is constrained.