In movies, surveillance is depicted as a few spooks sitting in an unmarked utility van sipping coffee, allegedly peeking into every aspect of a target's life. It sounds far fetched and unbelievable, but TEMPEST attacks represent a real world electronic surveillance technique dating back to the 1950s. Every electronic device emits RF (radio frequency) noise unless properly shielded. TEMPEST is simply the science of using antennas and detectors coupled with advanced reconstruction techniques to determine what those signals represent.

Previously, TEMPEST attacks saw great success against high RF targets like CRT computer monitors. Analysts could piece together the signals from the ray tube coils and remotely reconstruct what appeared on the screen. At the time, LCD monitors were thought to be more troublesome for TEMPEST detection owing to their reduced emissions. Security researcher Markus Kuhn recently shattered that illusion using refined TEMPEST techniques to remotely reconstruct an LCD image by analyzing signals leaking from the video cable. Proper shielding will restore security from such RF exposure. However, in a 2002 IEEE paper, Markus Kuhn demonstrated the reconstruction of a remote display's contents using nothing more than the ambient reflections of light on a wall (PDF).