The Federal Communications Commission (FCC) has issued the largest fine in its history—$34.9 million—against China-based C.T.S. Technology Co., for marketing signal-jamming devices to U.S. consumers.

The devices, commonly known as “jammers,” are RF transmitters that intentionally block, jam, or otherwise interfere with authorized communications. This includes cellphone calls, GPS systems, WiFi networks, and even first-responder communications, which presents a great danger to public safety. Only in limited circumstances involving federal law enforcement is it not completely illegal to market, sell, import, or use jammers.

C.T.S. allegedly marketed 285 models of jammers to consumers in the United States for over two years and also sold 10 high-powered signal jammers to undercover FCC personnel. The company’s website also falsely indicated that the jamming devices for sale were legal in the United States. According to Vamien McKalin at Tech Times:

The FCC is saying that CTS lied to consumers by stating its signal jammers were approved by the FCC, a move that likely caused a spike in sales.

Jacob Kastrenakes at The Verge goes on to say that some of the jammers had increased capabilities from the standard fare:

Various models it sold were allegedly able to block cell signals, WiFi, Bluetooth, satellite radio, and GPS, among others. Certain models were even effective up to half a mile away.

In determining the dollar amount imposed on the company, the FCC applied the maximum fine allowed to each model ($122,500). In addition, the FCC is ordering C.T.S. to cease all market activities of the jammers and to provide information about any persons or entities that purchased one of the devices. The entire enforcement action from the FCC can be read here.