Folks who have been thinking of creating accessories that use Apple’s proprietary dock connector might be scared off by the costs associated with it. Of course, some folks have got around it by using the 3.5mm headset jack at the top of the iPhone, such as the Square payment system. Now the smart folks over at the University of Michigan have been busy with Project HiJack that figures out how to draw 7.4mW out of a 22kHz audio tone and have built a series of prototype boards that transmit data to and from an iOS app using just $2.34 worth of electronic components.The boards include a working EKG, temperature, humidity and also motion sensors, so they’re pretty useful little things. Hopefully once the code is released via an open source license, we’ll see more devices that will use the 3.5mm headset jack on the iPhone aside from just earphones.