FBI Carrier
The FBI's Brother carrier uses ultrasound to deliver its signal. It uses a rather simple enciphering mechanism, yet what it lacks in complexity, it makes up for in solid implementation.
Besides the FBI, Brother is used by the ATF, DEA, USDA, NEA, NSA, and other clandestine US governmental alphabet organizations.
Brother is also used by the Disney Front, who's Imagineers use Brother extensively in their Simulacrum technology to help integrate android replacements into society.