However, if you are really concerned about it, the thing you are looking for is a
Faraday cage, which essentially shields anything inside it from electromagnetic fields or charges.
Yay physics!
Faraday cages don't do anything for magnetic fields? Compasses work in them for example (according to google). Electromagnetic fields are a field induced by alternating poles of magnetic or electric flows, I don't think we know the force that causes magnetism? (I could be completely wrong, my knowledge is a year old).
Faraday cages also protect against a large magnetic field, if you're going that way, get a leather case for it and then put it in the faraday cage (the leather case can block RFID/radio waves and microwaves afaik).