sonar sends sound from the speakers and the microphone listens for what comes back. every surface around you returns it a little later than the last, and the delay is a distance. each ring is one of those distances.

the rings have no direction. one speaker and one microphone can measure how far away something is and never which way it lies.

nothing leaves this device. no audio is uploaded, recorded, or kept. there is no server to send anything to; after loading, the page works with the network unplugged.

it reaches three to four metres in an ordinary room. the limit is not volume but the room itself — the sound’s own echo is still ringing when the quiet ones arrive. under about twenty centimetres it is deaf, because the sound going straight from the speaker to the microphone drowns everything that close.

it hears the nearest thing, which in a room may be a chair rather than the wall.

you can hear it. the sound sweeps five to sixteen kilohertz.