Abstract: A safety device for shutting off a gas valve at the detection of a gas leak has an add-on adaptor device having a first knob mounted over an existing gas knob and affixed thereto; a spindle coupled to the first knob, capable of rotating the fist knob, and the gas valve knob, between an open position and a closed position. A second knob is rotatably mounted substantially perpendicular to the spindle, and is provided with firm cantilever which is extended to provide a firm support along side the gas valve knob so as to cause rotation of the gas valve knob when the second knob is rotated in one direction. A spinning is attached to the second knob and is in a wound state when the second knob is parallel to the first knob when the first knob is in the open position, and in an unwound state when the first knob is in the closed position.