A pouch made of fabric for storing keys, with three separate detachable devices, ,, made of rigid material. The method comprises the following steps: projecting points of a next image to a three-dimensional space using camera parameters and depth map and projecting projected points from the three-dimensional space to reference image surface, thereby obtaining motion vectors for estimating changes between the next image and the reference image. This structure can avoid short-circuit between circuits and prevent insulating reliability from lowering.