This article presents a new method, which reduces costs and processing time for spatial object motion detection by focusing on the bare-hand motion that mimics computer mouse functions to allow the user to move the mouse pointer in real-time by the motion of his/her hand without any gloves worn, any object carried, or any key hit. In this article, the study of this topic is from the viewpoint of computer vision and image processing. The principals of the difference of the absolute differences (DAD) are investigated. A new method based on the DAD principles, which is conceptually different from all the existing approaches to spatial object motion detection, is developed and applied successfully to the bare-hand motion. The real-time implementation of the bare-hand motion detection demonstrates the accuracy and efficiency of the DAD method.