Im not so sure about how well this em detector would work. I have a feeling that at the lower altitudes where unmarked wires are more of a problem, this thing would be giving you warnings left and right, so the pilot may stop really paying it any heed. Although could probably also solve the problem by flying a tad higher.
Just my 2c guys, admittedly i dont have any experience flying in these kind of conditions (workin on my IFR). But I think that for this thing to give you any sort of warning it would have to be very sensitive, and that would also increase the amount of warnings you might get from say, regular appliances I would think.