Tweakers at Perceptive Development have built an external keyboard that works via a custom connection built for the headphone jack. It’s a progression of their previous project which added an RS232 serial modem interface to the iPhone’s headphone jack in/out. The headphone jack is one of the few interfaces that’s open in the official SDK. The microcontroller converts input from an external Targus IR keyboard to a terminal app that doesn’t require jailbreak. Pretty cool, but it’s still a bit more intensive than plugging in and typing.”]
Source: https://gizmodo.com/hackers-add-external-ir-keyboard-to-iphone-without-jail-5181973