Abstract: An anti-theft device fitted to the seat of the vehicle is provided for a motor vehicle. The seat containing a cushion, a frame and a back, including a mechanism for adjusting the angle of inclination of the seat back and comprising a fixed part and movable part. The fixed part and movable part located in the seat back and interact with each another with an additional horizontal axis and a lever. The movable part is adapted to forward rotation on the additional axis simultaneously with a gear-wheel, which holds the lever that locks the tilt-adjustment seat by the opposite end and driven by a pinion. The additional axle has the ability to horizontal displacement in the holding of its joints, forming an actuator of the locking device. The invention can be used to improve the seats ergonomics and for the bulk of transformations in the car.