Your MacBook microphone can detect ultrasonic frequencies above 22khz, though I'm not sure whether my observed ceiling is an artifact of the microphone, or of the speaker I was using to emit the tones.

In my informal tests, most people are unable to hear any tone above 20khz or so. This is discovered, naturally, by starting with the highest pitch tone I can generate at the loudest volume, and lowering the pitch gradually until somebody covers their ears and starts screaming. This is usually the youngest person in the room.

You can generate and receive audio using web audio APIs. Creating a browser extension to detect ultrasonic comma would be fairly straightforward.