It is illegal to make or sell or own radio hardware capable of operating on that spectrum, or modify other hardware to work on that spectrum, or hint to your users how they might modify your product to work on that spectrum, unless you are a licensee or have permission from one. Even Motorola can&#x27;t take its new basebands out of RF-isolated testing facilities before FCC approval.<p>Theoretically calls are encrypted, however security researches have shown vulnerabilities due to old&#x2F;incorrectly applied primitives. Not sure exactly which protocol versions this applies to. Stingray might just have asked nicely for the keys.<p>Commercial IMSI-catchers (made with the cooperation of carriers?) do exist, and there are some hobbyist proofs of concept. It is very hard to get caught doing passive receiving.<p>Transmit in a way that catches the eyes of carrier network engineers, though, and the federal government will come knocking with criminal charges.<p>FCC makes exceptions to most things for official purposes. For example, government installations can be licensed to operate cell phone jammers