The invention relates to a mechanical sprung anti-backoff device, capable of fixedly immobilizing or releasing a manual control handwheel (4) and a motor acting on one and the same rotation shaft, comprising a cylindrical spring (7, 16), a cylinder (9, 17) mounted so as to rotate on the rotation shaft, the spring being able to rotate with the cylinder, turns of the spring being in contact with a surface of the cylinder and its ends being capable of coming into contact with the handwheel. The ends of the spring (7, 16) are curved inward or outward, the handwheel (4) may act on the curve of one or other of the ends of the spring (7, 16), and the rotation of the spring (7, 16) is limited by a stop acting against one or other of the ends of the spring. Application can be to manual control and motorized control valves, for example on fluid pipes.