Next time you pass someone on the street who appears to be talking to themselves, they may literally have voices inside their head…and be a highly trained soldier on a dangerous mission. The Pentagon has inked a roughly $10 million contract with a California company to provide secure communication gear that's essentially invisible.

Dubbed the Molar Mic, it's a small device that clips to your back teeth. The device is both microphone and "speaker,"  allowing the wearer to transmit without any conspicuous external microphone and receive with no visible headset or earpiece. Incoming sound is transmitted through the wearer's bone matter in the jaw and skull to the auditory nerves; outgoing sound is sent to a radio transmitter on the neck, and sent to another radio unit that can be concealed on the operator. From there, the signal can be sent anywhere.