A quick search indicates that <100 dB ultrasonic is legal. So make a phone cover that generates ~80 dB spread spectrum ultrasonic. That should be enough, right?
And humans. These things aren't really ultrasonic because phones and computers can't transmit ultrasound (why would they need to?).
This is something I was curious about. Sure, if you're doing serious audio editing and such, you might sample at e.g. 96 kHz, and I wouldn't be surprised if Android also allows that. But does this really not get band-limited at any point in the stack?
Poor me, I can hear the ultrasonics generated to repel dogs and cats...
Yeah, apparently you're supposed to lose that ability in your mid-20's, but I still hear them loud and clear at 28...
I used to hear ultrasounds fairly well. It goes away unfortunately.