I agree Ela, the problem with collars, even if you are willing to use them, is that they often end up draped over a bush or something similar so all you would be tracking is the collar - nice if it saves you having to buy collars all the time, but the priority here is finding the cat, not the collar - sorry saxa but you need to go back to the drawing board if you are seeking a practical solution. If, however, it is simply an assignment for your design course, as you originally suggested was the case, then good luck with the project.