Journalist David Hambling has written in New Scientist (UK, center-left, popular science magazine) and Wired (USA, center-left, popular technology magazine) about the on-going development of a technology to beam sounds into a person's head using microwaves. This technology is not immediately of practical benefit, judging by the articles, but it is a bit of fun reading.
What I took away from these articles is that there are potential (probable?) health risks when used a high power levels, such as in crowd control applications, so researchers are looking at where it might be useful in low power applications - advertising is mentioned, of course.
As an aside, I noticed the continuation of a pattern that seems to appear with all less-than-lethal "weapons" (i.e. those technologies that seek to incapacitate, drive-off, etc, rather than kill the subjects) - namely, once you label a technology or technique as "less than lethal", this seems to consistently bring with it the hard requirement that it be 100% less-than-lethal in all conditions. Taken to its obvious conclusion, this pattern will make most, if not all, less-than-lethal development projects go bust at some point, for better or worse.