Subdermal implants or subdermals are special communication devices placed in the coclear (or inner ear) and vocal cords.
Subermals are used by specific United States of America government agents so they can receive radio transmissions from their handlers via a special earpiece (i.e. "cochlear implant") from virtually anywhere without the risk of being heard by surrounding enemies as well as voice messages from them via satellite. It provides satellite tracking on the user as well, giving positional data for the agent's handlers. They can also communicate with their handlers via a PTT (Push-To-Talk) transmitter that translate data for use with a voice synthesizer located at the agent's headquarters. The only drawback is that the device can malfunction while underground and the signals can be picked up by the enemy.