A ring tone adults can't hear
Have you heard about this? https://www.nytimes.com/2006/06/12/technology/12ring.html?ex=1307764800&en=2b80d158770dccdf&ei=5088&partner=rssnyt&emc=rss
The irony is that it's an offshoot of a "teenager repellent" security device.
Poetic.
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(Okay, not quite speech related. But certainly audio and communications related.)