Abstract: The device is intended to cut-off the supply of electric power to a motor (4) automatically when this latter is locked rotationally under the action of a mechanical resistance.This device comprises balls (5) coupled for rotation with the motor (4) and displaceable under the action of the centrifugal force generated at the time of rotation of this motor, these balls (5) being in cooperating relation with an electric contact (9) in order to put the electric power supply of the motor (4) in circuit when this centrifugal force attains a certain threshold value and in order to put this supply out of circuit when this centrifugal force drops under the action of the mechanical resistance set up in opposition to the torque exerted by the motor.Utilization in particular in automatic devices for the control of opening and closing of garage doors.