I have noticed that when I make calls on Skype, I sometimes hear a small echo of my voice. This has a remarkably discombobulating effect, making it almost impossible to continue speaking.
I learned that a Japanese company has used this effect to create a speech jamming gun that you can use to silence speakers whom you find annoying.
I am not sure what would happen if people started using it at public meetings. If only it could be made to work when you point it at someone speaking on TV…
Talking of TVs, you could use the device known as TV B Gone that can be used to surreptitiously turn off TVs in public places, such as airports, when it is impossible to avoid them.
It is likely that use of both these devices is illegal.