Magnetic fields are not blocked by common materials such as the walls of buildings. Magnetic fields Electric fields arise from voltage. An electric field can be present even when a device is switched off. Field strength decreases with distance from the source. Most building materials shield electric fields to some extent.
Magnetic fields arise from current flows.
Magnetic fields exist as soon as a device is switched on and current flows. Field strength decreases with distance from the source. Magnetic fields are not attenuated by most materials. Plugging a wire into an outlet creates electric fields in the air surrounding the appliance. The higher the voltage the stronger the field produced.