Jamming Speech with Recorded Speech
This is cool:
The idea is simple. Psychologists have known for some years that it is almost impossible to speak when your words are replayed to you with a delay of a fraction of a second.
Kurihara and Tsukada have simply built a handheld device consisting of a microphone and a speaker that does just that: it records a person’s voice and replays it to them with a delay of about 0.2 seconds. The microphone and speaker are directional so the device can be aimed at a speaker from a distance, like a gun.
In tests, Kurihara and Tsukada say their speech jamming gun works well: “The system can disturb remote people’s speech without any physical discomfort.”