Van Eck phreaking is a form of digital espionage whereby an eavesdropper detects and analyzes digital signals using equipment that can pick up the electromagnetic emissions put out by a cathode ray tube (CRT) or LCD display. This makes it possible for someone to read the images on another person's display from a distance.

There are ways to obscure or reduce display emission in order to thwart Van Eck phreaking, but they are not commercially viable because the security risk that Van Eck phreaking poses to the general public is considered to be very small. This is because Van Eck phreaking requires specialized knowledge and decoding equipment that is not widely available. Highly sensitive computer networks do, however, use Faraday cages to prevent any possibility of a breach via Van Eck phreaking.