It depends on distance from EMP device. For less than kilometer (mile), you need Faraday cage and all io devices inside it, and/or protected by NATO standard p

It depends on distance from EMP device. For less than kilometer (mile), you need Faraday cage and all io devices inside it, and/or protected by NATO standard protection, and all these measures does not guarantee. For tens kilometers or more, electrically simplest surge filter will be enough, sure good to have UPS, but after first few seconds, this will only affect radio communications (more long wave, less UWB/microwave, like wifi), because extremely disturbances of ionosphere. To be exact, will be up to 20 hours strong low frequency waves (from hundreds Hz, up to tens MHz), they will affect power lines, railroad signaling (they are just few tens volts), copper networks, similar techs. As I know, ionosphere is transparent for 100+MHz, on which modern computers operate.