All it takes is a $ 1 antenna and a readily available software-defined radio
A researcher from Ben-Gurion University in the Negev successfully detected UDP packets from CAT6 cabling and decoded them into human-readable text, without spending more than $ 30. The attack can be executed successfully with a variety of software-defined radios, as most can scan and demodulate broadcasts at around 250 MHz, a frequency that can escape poorly insulated LAN cables.
The experiments they conducted required their receiver to be within 4 meters, but this distance limit was due to the inexpensive antenna they used, a more specialized antenna would have to have a much longer range. For their tests, they had to slow down UDP packets to successfully capture and decode the data, but there’s no reason malware couldn’t be designed to do this on a system or to reassure you that a more refined technique would be able to capture data flowing at normal speed.
The PDF of the research paper referred to by The Register provides a long list of similar ways to defeat a dead hole system, as well as details on the LANtenna attack, if you really want to scare yourself this Friday.