On iPhones running iOS version 7 or later, users can install to assign behaviors tilted his head with a corresponding command.
To enable the "Madness", you need to go to Settings (Settings)> General settings (General)> Accessibility (Accessibility)> Control switches (Switch Control).
Then, set a switch (Switch), select the source as camera (Camera), gestures as Tilt your head to the left (Left Head Movement) or tilt your head to the right (Right Head Movement).
This step will be a series of Action (Action) for your choice. Which, ideally, activated virtual assistant Siri. Because after activating Siri you can continue to control iPhone by voice interaction with a wider range very much. After setup, you just shake your head left or right Siri iPhone will open to serve you.
In some cases, this feature also helps users interact with iPhone quite effective, such instead activate Siri, you can set so that when the iPhone will shake your head left to go back, to the right to come next page...