In exemplary implementations of this invention, a radio signal is transmitted between a transmitter and a receiver. Either the transmitter, or receiver, or both, have a directional antenna. When organic tissue passes between (or is stationary between) the transmitter and receiver, the tissue causes a reduction of the received signal strength (RSS) of the signal, as compared to a baseline RSS. The larger the amount of tissue, the greater is the reduction of the RSS. By analyzing the degradation of the signal, information about organic tissue between the transmitter and receiver may be determined. For example, the number of persons passing through a physical threshold may be determined. Or the fact that one person is walking faster than, and catching up with, a second person as they pass between the transmitter and receiver may be determined.