Personal Mute

This device would consist of a fully-covering mouthpiece, some headphones and a few I/O jacks for various devices. The mouthpiece prevents sounds of a certain volume or lower from emanating, perhaps through the use of destructive interference (ITPUET?). However, the vocal sounds can still be transmitted into headphones, cellphones, recorders or radios. The practical upshot is that you can speak in normal tones and only you and the gadgets hooked into the device will hear your voice. This will spare others from your meaningless jabber and save you some of the embarrassment of, say, practicing singing or a foreign language in public.

This device will feature an emergency override which allows shouted sounds to take on their proper volume and an "unmute" button for quieter conversation.