> It works best with a small hardware extension (a small speaker/headphone) to focus the sound on the mic, making it silent its surroundings. An idea how to build it is found in the Menu.

Great when you know where the microphone is but can’t leave the area for a private chat; not so useful when the microphone is any nearby substance that reflects some wavelength and which vibrates enough when exposed to sound that the reflected light can be decoded.