Apple's proprietary dock connector may keep would-be peripheral manufacturers at bay, but if you want to build your own iOS companion devices, there's another way. You might have noticed that the Square credit card reader uses Apple's 3.5mm headset jack to transmit power and data at once, and gadgeteers at the University of Michigan are busy open-sourcing the same technique for all the DIY contraptions you can dream of. Project HiJack has already figured out how to pull 7.4
