Abstract: A motion detection camera system which may be used as a security camera includes an active pixel imaging system operable in a video and differential mode connected to a mode activation circuit that controls the imaging system mode. In the video mode, the imaging system generates an output signal containing information of a viewed area on a frame by frame manner. In the differential mode, the imaging system generates a differential output signal containing information consisting of the differences in the viewed area between adjacent detected frames. Normally, the imaging system camera is operated in the differential mode. If no motion occurs in the viewed area, the corresponding differential output signal representing the interframe differences will have a constant signal level. Upon detecting that the differential output signal deviates by greater than a threshold level indicating motion in the viewed area, the mode activation circuit causes the imaging system to operate in its video mode.