Serious ethical issues are raised by some of the potential uses of hypersonic sound, because the projected messages are imposed upon people against their will, and could perhaps be used to subtly manipulate behaviour.

THAT is creepy!

creepy is putting it mildly.....maybe I'm being paranoid but I always imagine things like this being used for negative purposes.....

Yowza. I am impressed with the amount of possibility here as well as the amount of dread I feel.

Two immediate things come to mind ...

1. "hearing voices" as a legal defense - just took on a whole new meaning.

2. Someone could beam voices into someones head. In an attempt to control them, or make them think they are mad. Many suspense/horror films use this idea.

that is seriously creepy, but I don't think it's any more of an ethical issue than any other type of sound-making ad. You don't have a choice to listen to those either it's the same type of manipulation if you hear it alone or everyone hears it.

I was just about to say that, kitty. Isn't all sound "imposed upon people" whether they will it or not?

It's the surreptitious manner of this technique that's icky.