[baronep]

The sensor is retro-reflective which means that it measures the reflective properties of whatever it is pointed at. If you turn the sensitivity all the way in one direction, it will trip if it has barely any reflection, however, in order to make these sensors work, you have to measure a slight difference between the carpet and the tape that they put on the ground (meaning that unless you have the exact same carpet that they use at competition, you will have to calibrate once you get there.) On our setup, the line sensors are only 2-3 inches off the floor.