You generate a potent magnetic field. You set off metal detectors, fixed or portable. You cannot use a magnetic compass because it will always point to you. You take a -2 penalty on Computer Use, Craft (electronics), or anything else that involves electronics being placed within 5 feet of you. Any magnetic recording medium (tapes, hard disks, credit cards with magnetic strips, etc.) must make a Fortitude save (DC 10) every time you handle them, or the data is permanently and irretrievably scrambled.