Abstract: A safety device fitted with window curtains comprising a stopper safety hanger, a single wheel safety hanger and several safety clamps. When an object is caught by the curtain string, a small copper ball of the stopper safety hanger goes sideways from a copper wheel contracted by a steel spring wire making the copper wheel drop by its weight and loose the curtain string. A single wheel hanger is fitted for easy, balanced and convenient operation. Two string safety clamps automatically spring out from the two hangers by action of the spring clamp. The loosened curtain string separates the entangled object from danger guaranteeing safe operation of window curtains.