In brief: Amazon and other retailers are being investigated by the FCC over allegations that they market and sell unlawful electronic devices designed to block or disrupt signals sent by other electronics. It follows an investigation into the sale of radio frequency jammers, which are advertised as drone deterrents or privacy tools.

Earlier this week, NBC News investigated the number of retailers offering radio frequency jammers despite them being illegal to sell and operate in the United States.

According to the FCC, federal law prohibits the operation, marketing, or sale of any type of jamming equipment that interferes with authorized radio communications, including cellular and personal communication services, police radar, and global positioning systems. There are no exemptions for use within a business, classroom, residence, or vehicle, and local law enforcement agencies do not have independent authority to use jamming equipment.

NBC said it found nine independent sellers on Amazon selling the jammers, as well as online stores based in China and domestic companies selling drone-related equipment. A Minnesota-based company was offering a portable anti-drone "RF jamming unit" for $2,999 on its website, supplied by China-based company Tatusky. The device is described as resembling a shotgun, easy to use, and with a 1-2 kilometer (0.6 – 1.2 mile) range.

Following the investigation, Jonathan Uriarte, Director of Strategic Communications at the FCC, said that the agency is investigating Amazon and other retailers for potential violations of Commission rules related to the sale and marketing of equipment without proper FCC authorization.

It was reported last month that police in Minnesota were warning people of burglars who have been using Wi-Fi jammers to temporarily disable homeowners' connected security systems, including surveillance cameras. These jammers don't actually block signals, but overload the wireless networks so the real traffic cannot get through to the devices. While this was a spate of similar incidents stretching over six months, jammers have been used by criminals for years to circumvent the likes of Ring video doorbells.