I heard this on NPR recently. A shopkeeker in the UK was afraid or annoyed about some young people spending time outside of his store. An inventor applied a high-pitch frequency to the situation, one that would repel the teenagers, but that adults cannot hear. This worked. (The next part of the story is that the teens used this sound as a ringtone and can now call each other during class. Nice work, kids.)
The story was supposed to be one of those feel-good what will they think of next? sort of interviews. Melissa Block was friendly and appropriately interested in the science of the thing (since NPR listeners are predominantly nerds), and the inventor was appropriately proud of his solution to this pest problem. There were no questions about what else this technology could be used for, no consideration about where teens are supposed to go when all shopkeepers decide to electronically alienate this age group. The inventor did not reveal plans to figure out other frequencies for other people groups.
Maybe sadder still, later in the interview, the inventor's teenage daughter explains the bit about the cell phones. She and her father seemed to get along fairly well. This man may not have considered that the day could come when his daughter would be forced from a space against her will by his device. I guess the listener to this story is not supposed to ask about the application of such technology. We are supposed to rejoice that it exists and that our lives will continue to improve.