Every electronic, electro-optical, or electromechanical device—including cell phones and hand-held computers—emit some type of electromagnetic signal. This emission exists even if the device was not developed to be a transmitter. It is a well-known fact that cell phones are not permitted to be engaged on airplanes or in designated hospital areas because their signals could interfere with vital equipment designed to be sensitive to electromagnetic radiation (EMR).

Since World War II, intelligence experts have reported that the electromagnetic radiation leaking from devices could be intercepted by enemies of the State and that secret messages could be reconstructed using special devices. The term Tempest, or Tempest radiation, was coined by the U.S. military in the 1960s to indicate the classified study of what was then known as “compromising emanations.”

Today, the exploitation of such emanations is referred to as van Eck phreaking, named after Wim van Eck, a Dutch computer specialist who in 1985 published his paper entitled “Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk?”

Presently, government agencies concerned with such security issues are constructing “safe rooms.” Using metallic shielding, experts can block the EMR so that it cannot emanate from the safe room. Alternatively, experts can ground the signals so that they cannot be intercepted. A number of manufacturers market products that are purportedly safe from van Eck phreaking.

See Also: Eavesdropping; Risk; Tempest Equipment.