Interesting tech. From New Cellphone Headset Cuts Background Noise, Improves Voice Clarity:
Aliph’s Jawbone technology, which grew out of research the company did for the Pentagon, relies on two kinds of microphones. Standard microphones transmit your speech and detect background noise. A special contact microphone, which rests against your cheek, uses vibrations in your bones to determine exactly when you are speaking.This latter mike, which Aliph calls a ‘voice activity sensor,’ allows the Jawbone headset to distinguish your voice from background noises much more accurately than a normal cellphone headset can.
Like many other acoustic systems, the Jawbone includes special chips and software that attempt to enhance voice frequencies and reduce background frequencies. But because the contact microphone lets the device know precisely when you are speaking, it is able to apply these digital filters more efficiently and successfully.
To accommodate the multiple mikes, the Jawbone’s design is quite different from most headsets, which aim to be almost invisible. The Jawbone is light but large and quite visible, with a shiny aluminum piece that extends from your ear to your cheek. On one end of this prong is an earpiece, and on the other end is the contact mike that rests against your face. There’s also a second part, a control unit that clips to a shirt or belt, or can tuck into a pocket or purse.