I am doing a project in work. I am in the army and i am looking at making a PIR sensor to detect the movement of enemy troops outside of a harbour area, at a max distance of 20 feet and once triggered to alert the sentry positon covertly. Is there anyway or component that can be used in conjuction with the sensor to give an indication of the distance as well? So for instance something as simple as the closer the distance the more LEDs light up. Any help or ideas would be much appreciated.