In a classical video monitoring system, though for most of the time the captured images contain no relevant information, it cannot prevent the monitoring system from useless power consuming for image processing. To improve this, one technique proved to be effective for a video monitoring system to reduce its power consumption is based on macro-pixels or blocks of pixels for region of interest (ROI) finding. The key feature necessary for ROI finding corresponds to motion detection. To be able to implement ROI detection, two CMOS-based motion detection circuits are proposed in this paper. Both are designed and optimized to have fewer transistors' number, lower power consumption, higher sensitivity and better uniformity detection within the designed input common mode range.