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.

“Essentially, what you are doing is receiving the same type of auditory information that you receive from your ear, except that you are using a new auditory pathway — through your tooth, through your cranial bones — to that auditory nerve. You can hear through your head as if you were hearing through your ear,” said Peter Hadrovic, CEO of Molar Mic creator Sonitus Technologies. He likened the experience to what happens when you eat a crunchy breakfast cereal — but instead of hearing that loud (delightfully marketable) chewing noise, you’re receiving important communications from your operations team.

Your ability to understand conversations transmitted through bone improves with practice. “Over the period of three weeks, your brain adapts and it enhances your ability to process the audio,” said Hadrovic. But even “out of the gate, you can understand it,” he said. (more below)