Note that this technique has a pretty neat malicious use case: bridging air gaps, in a way that removing/disabling wireless chips won't stop. You'd have to have already installed malware to the airgapped machine, of course, but once that's done, chances are it'll frequently be in range of (presumably easier to compromise) Internet-connected machines, and ultrasound allows slow but bidirectional communication.<p>This was alleged in 2013 to have been done in a piece of malware dubbed "badBIOS", but said malware is likely imaginary.<p><a href="http://arstechnica.com/security/2013/10/meet-badbios-the-mysterious-mac-and-pc-malware-that-jumps-airgaps/" rel="nofollow">http://arstechnica.com/security/2013/10/meet-badbios-the-mys...</a>