Abstract: Disclosed is an automatic video intrusion detection system. The system monitors a given area such as between two parallel fences. The image of the given area is divided into an array of cells each approximately equal in size to the image of a man. The video for each cell is integrated, digitized and stored in an array. Changes in cell values are detected and tracked so that changes in, say, 3 adjacent cells in a given direction, indicate an intruder. A microcomputer implements a tracking algorithm. Filtering discriminates against light level changes. The system is simpler than a known one which analyzes grey values of thousands of points in a video field.