The invention provides an anti-theft device for motor vehicles, comprising an immobiliser bar (10) for fitting across a steering wheel so as to project generally radially from the steering wheel to prevent or limit rotation thereof by contact with other parts of the vehicle, and a locking arrangement (12) mounted at one end of the immobiliser bar for locking the immobiliser bar onto the rim of the steering wheel at one side thereof. The locking arrangement comprises a pair of hooks (16) pivotably connected to the immobiliser bar for movement around an axis perpendicular to the immobiliser bar between an open position in which the free ends (26) of the hooks are remote from the bar for engaging over the steering wheel rim and a closed position in which the free ends of the hooks lie adjacent the immobiliser bar for securing the immobiliser bar onto the steering wheel rim, and a locking assembly (3) for rigidly securing the hooks in the closed position.