Seeing as apple are strict on what devices that may get power from your trusty iPhone by ways of the dock connector patient! It seems some nice people at the University of Michigan have decided that just won’t do, By ways of using power from the 3.5mm headphone hack. How does this work you ask, Well seeing as credit card reader for iPhones uses the 3.5mm for not only power but data aswell, It seems there is much more to be had with the 3.5mm then sound.
Project HiJack has already figured out how to pull 7.4 milliwatts out of a 22kHz audio tone, and built a series of prototype boards (including working EKG, temperature, humidity and motion sensors) that transmit data to and from an iOS app at up to 8.82 k baud. Check out the video below and then head over to Project HiJack’s website.