This is a very cool demo. There are a couple of ways to improve this technique, improve accuracy, reduce power, and improve noise rejection.<p>The biggest wins are in improving the waveform from this one (called "continuous wave" or CW in the radar/sonar literature) to one with more bandwidth. One option is to sweep the frequency continuously (FMCW) or with breaks. Another option is to switch from this continuous noise to pulses of noise, just turning the sound on and off. Pulsing like this increases bandwidth (because the "turning on and off" introduces higher-bandwidth edges) very simply. Modulating the frequency during the pulse helps more, creating a wolf-whistle like "chirp".<p>Doing the signal processing for these alternative waveforms is a little bit trickier than the technique this page uses. It can be done in the time domain with correlation, or in the frequency domain with the the FFT and simple multiplication.