We describe a novel battery-powered vision sensor developed to support surveillance and crime prevention activities of the Law Enforcement Agencies (LEA) in isolated or peripheral areas not equipped with energy grid. The sensor consists of a low-power, always-on vision chip interfaced with a processor executing visual tasks on demand. The chip continuously inspects the imaged scene in search for events potentially related to criminal acts. When an event is detected, the chip wakes-up the processor, normally in idle state, and starts delivering images to it together with information on the region containing the event. The processor re-works the received data in order to confirm, to recognize the detected action and in case to send the alert to the LEA. The sensor has been developed within a H2020 EU project and has been successfully tested in real-life scenarios.