https://www.theregister.co.uk/2018/05/25/sonic_firewall/

Boffins in Austria have developed a defense against acoustic cookies, a form of ad tracking by which smartphones can send and receive data using sounds people can't hear.

App developers can implement ultrasound data transfer on their own or using various SDKs, such as XT Audio Beacons or Lisnr, or the Google Nearby API.