>It's visible in the visible spectrum and hearable in the human hearing range, which means that you can build detection and tracking systems in those wavelengths instead of pretending that its invisible because its hard to detect at radar wavelengths.

Most anti aircraft radar works by sending out radar pulses and measuring the return. Visual spectrum light is scattered significantly by the atmosphere. It is a physics problem and visual range is just not as good of a medium as HF, UHF, VHF etc radar. Which there are multiple over-the-horizon radars with ranges in the hundreds of miles. And that is before we add in clouds, fog, smoke, snow, or you know, darkness, where radio waves easily penetrate. Visual detection needs far more contrast than radio wave detection. Optical detection is just not well suited.

As for using sound to detect and track an object coming at you at faster than the speed of sound, I think it encapsulates this entire comment’s level of thought and insight.