A Faraday cage, is a sealed enclosure that has an electrically conductive outer layer made from material such as steel or copper and an inner non-conductive layer made from material such as cardboard or insulation. When closed, the Faraday cage blocks external static and non-static electric fields by channeling electricity through the outer conductive layer.
A Faraday cage will protect your electronic devices from an electro-magnetic pulse (EMP) from the sun or a terrorist attack. If your electronics are not protected in a Faraday cage, they will no longer work after an EMP. A Faraday cage is fairly cheap and easy to construct and is something that all preppers should consider building.
You can make a Faraday cage out of any steel file cabinet or box, below is an excellent video by LDSPrepper that shows you how to go about it. So check out the video and make one for your valuable electronics.