Well, the rub of that is that magic also effects mechanical things at times too. Ultimately, the logic of how magic impacts technology is, well, magical.
I'm not meaning that to be handwavey - rather I mean that the logic is something very different from the norm, and as such, things that might seem to make perfect sense may not be applicable at all. That said, if you're just a guy who's knowledgeable about magic and want your machine to not get fried maybe you put it in a circle, or behind a strong threshold, or over running water. Buy into the logic of magic, and things open up.
Setting that aside, I don't see such a thing making it into the book, but at the same time, it's something that could make for a really awesome game element. The specifics of the device (and the first one will be a gun: the first one is *always* a gun) don't interest me as much as what its existence _implies_. It suggests that people with the *means* and the *understanding* necessary have made this happen, and once that's been done, what else might they do? Whant mage-killing bombs? Set up a stack of TNT with a sophisticated electronic device that's keeping it from exploding. Merry Christmas. A little tweaking of the setting and you could have a great technology vs. magic game. It wouldn't be Dresden, but it would probably be cool.
See, on the surface, it seems like things are tilted strongly in favor of magic over technology. Magic can do things like generate shields, kill remotely and most of all, it's directly disruptive to technology. But that's only half the story. Setting aside the numerous advantages in technology, like unskilled use, ubiquity and sheer variety of application, one key fact remains - the greatest advantage of magic is the ignorance of the populace as a whole. If people understood some basic principles, like cirlces, thresholds, water, the importance of props and so on, the conflict would grow quickly lopsided. In setting, the best illustration of this is the impact of Bram Stoker's writings on the health of the Black Court. Just imagine if Mr. Butcher was a guy with a bone to pick with the Wizards of the world - think of how good a how-to manual the Dresden files would be.
(As an example, one of Harry's greatest strokes of luck is that he has yet to face an opponent who, upon capturing him, has not stripped him naked and thrown his every posession into the nearest blast furnace, and tucked away a few hair trimmings for good measure).
Anyway, this is a long way of saying that, no, you probably can't harden a device agaisnt magic the same way you can against EM, but at the same time, if you're willing to think a little crazy, you can make the rules of magic work for you.
-Rob D.