A Faraday cage is an enclosure with no apertures (holes, slits, windows or doors) made of a perfectly conducting material. No electric fields are produced within the Faraday cage by the incidence of external fields upon it or by currents flowing on the perfect conductor; that is, the perfectly conducting enclosure is a perfect electromagnetic shield. If no electrical energy sources are within the Faraday cage, then there will be no electric fields within, since none can penetrate the conducting enclosure. The Faraday cage can be any shape of closed surface; ... 
A Faraday cage can enclose an arbitrary volume, so several rooms or buildings, which alone would each be a Faraday cage, ... 
Since a perfect conductor is an idealization unavailable in nature, perfect Faraday cages do not exist. However, extremely good Faraday cages are constructed for electromagnetic experiments; they are commonly called "screen rooms." Early (and still common) screen rooms were made of copper mesh screen with a somewhat tighter mesh than typical aluminum window screen. Screen rooms are also made of welded sheet aluminum or sheet steel. For all screen rooms, special attention is given to electromagnetic sealing of closed doors and to metallic penetrations for power or communication. 
Faraday cages are often put to a dual purpose: to block electric fields, as explained above, and to block electromagnetic radiation. The latter application is known as RF shielding. 
TEMPEST is a U.S. government code word for a once-classified set of standards for limiting electric or electromagnetic radiation emanations from electronic equipment such as microchips, monitors, or printers. It is a counter-intelligence measure aimed at the prevention of electronic espionage. 
In telecommunication, the term electromagnetic pulse (EMP) has the following meanings:
- The electromagnetic radiation from an explosion (especially nuclear explosions) or an intensely fluctuating magnetic field caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the electronic or explosive device or in a surrounding medium. The resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges. The effects are usually not noticeable beyond the blast radius unless the device is nuclear or specifically designed to produce an electromagnetic shockwave.
- A broadband, high-intensity, short-duration burst of electromagnetic energy.
Note: In the case of a nuclear detonation, the electromagnetic pulse consists of a continuous frequency spectrum. Most of the energy is distributed throughout the lower frequencies between 3 Hz and 30 kHz. 
See also , , , , and .