A Japanese research team has developed a device that can compel the overly talkative to shut their mouths and let somebody else get a word in edgewise. Before you start pulling out your pocket Bill of Rights, understand that researchers Kazutaka Kurihara and Koji Tsukada haven't developed a weapon, it's more of an etiquette enforcer - with extreme prejudice. Their device processes the speech of an overly loud person, then computes and adjusts the frequencies and sends their own words back at them, modulated in such a way that they become instantly confused and therefore more likely to shut their traps already.
Their "SpeechJammer" device uses a phenomenon known as delayed auditory feedback, sending someone's own recorded voice back at them in a strategic gap that causes most people to pause in their speech. If you've ever been on as phone call where you can hear your own voice in the receiver a second or two late, you know what that feels like. The researchers developed the tool to gently encourage patrons of traditionally quiet venues, like libraries or art galleries, to take the conversation somewhere else. The SpeechJammer is completely harmless, but you wouldn't know by looking - it's even got a laser guidance system.
That's thinking a little small, though: imagine the possibilities is movie theaters or cable TV political debates. If someone takes too long to answer a question (or does so in a manner that's less than polite) you could point the SpeechJammer their way and almost literally derail their train of thought. Currently the two graduate students are refining their techniques; at present it needs quite a bit of volume to achieve the desired effect, somewhat defeating their original purpose. Even so, I can't wait until someone embeds this tech into a smartphone.