System and device for window covering

A window covering system, comprising:

• a headrail, a bottom rail, a covering material, and a control unit, wherein the covering material is positioned between the headrail and the bottom rail, and the control unit is positioned outside of the headrail;
• and a first rotating unit positioned within the headrail, wherein the first rotating unit is configured to be driven to rotate in a first direction when the bottom rail descends to expand the covering material;
• and
• a locking device coiled to the first rotating unit, wherein the locking device comprises a fixed end and a free end, and the fixed end is fixed relative to the headrail, and wherein the locking device is configured to provide a restriction force to the first rotating unit in order to restrict the first rotating unit from rotating in the first direction, as well as to restrict the bottom rail from descending;
• and
• an actuating device comprising a pushing part, which is positioned corresponding to the fixed end and configured to operate with the control unit simultaneously, wherein the control unit is configured to drive the pushing part of the actuating device to push the free end of the locking device to move in order to remove the rotation restriction to the first rotating unit by reducing the restriction force provided by the locking device to the first rotating unit;
• when the rotation restriction to the first rotating unit is removed, the bottom rail descends by gravity to drive the first rotating unit to rotate in the first direction.