Y.T. does not really get this, but these small antennas are millimeter-wave radar transceivers. Like any other radar, they are good at picking up metallic objects. Unlike the radar in an air traffic control center, they can rez fine details. The rez of a system is only as fine as its wavelength; since the wavelength of this radar is about a millimeter, it can see the fillings in your teeth, the grommets in your Converse high-tops, the rivets in your Levi's. It can calculate the value of your pocket change.