This paper describes a real-time application programmed into Wi-FLIP, a wireless smart camera resulting from the integration of FLIP-Q, a focal-plane low-power image processor, and Imote2, a commercial WSN platform. The application, though simple, shows the potentiality of the reduced scene representations achievable at FLIP-Q to speed up the processing. It consists of detecting the active regions within the scene being surveyed, that is, those regions undergoing thresholded variations with respect to the background. If an activity pattern is prescribed, FLIP-Q enables the reconfigurability of the image plane accordingly, making its detection and tracking easier. For each frame, the number of active regions is calculated and wirelessly reported in real time. A base station picks up the radio signal and sends the information to a PC via USB, also in real time. Frame rates up to around 10fps have been achieved, although it greatly depends on the light conditions and the image plane division grid.