A video camera system includes: a video sensor providing image data; a low power imminent event detector coupled to the sensor which receives the image data from the video sensor and processes the received image data to detect changes in the image data and thereby detect an imminent event and produces an event signal on detection of an imminent event; and a main event processor also coupled to the video sensor to receive the image data, the main event processor being a higher power device than the imminent event detector, the main event detector having a dormant mode in which the main event detector consumes little or no power and a fully active powered up mode, wherein: the main event processor switches from the dormant mode to the fully active mode in response to the event signal.