A microwave oven may be used as a Faraday cage. A Faraday cage is an electrical barrier that protects its contents from EMPs. A tightly sealed metal garbage can (as opposed to an ammo can or a metal safe) is the most basic alternative (other options include a tin can and a military safe).
A faraday cage is simple to make, but because we don’t know how much damage an EMP weapon might do, it’s impossible to say which technologies will survive. All we can do now is trust the judgments of those who have studied the issue.
Follow these steps and hope for the best.
Determine how much space you’ll need for the box. Calculate how much room each of your valuables will take up and see whether they require a specific size box. Shortwave radios, walkie-talkies, key medical equipment (such as a glucose meter), and spare electronic components for your generator and car are examples of common things.
Batteries are not harmed by EMP, so they don’t need to be included in your stash.
Choose a box or container that is as airtight as possible. Any gaps will deactivate the grounding.
Wrap your box in aluminum foil to seal it properly. Make sure the body of the box and its lid are completely enclosed.
Every seam needs to be firmly tacked down. You may use regular tape for this, but aluminum or copper tape will offer greater security.
To prevent your electronics from coming into contact with any of the foil or metal tape, line the inside of the box with cardboard.
Place your items inside and seal the lid firmly.
Hope that no one ever activates an EMP.