[camtarn]

This one's come up on HN a couple of times before - sensing EM fields via a fingertip-embedded magnet: http://www.wired.com/gadgets/mods/news/2006/06/71087?current...

More sensitive EM field detection could be vaguely useful, but to be useful it would probably require a bit of pre-processing (e.g. scaling the entire frequency range of the currently used EM spectrum into a range we can hear, see or feel) and maybe some protocol-specific hardware (decoding radio, video, wireless etc).

Other interesting candidates for extra-human senses beyond just increasing the range and sensitivity of existing senses would be EM/light polarization (insects can see polarization in the sky, so they can navigate by the sun's direction even when it's hidden by clouds) and magnetic field direction (which exists in bacteria, invertebrates, and birds, and may exist in some mammals.)