Apparently, this feature has been available since iOS 7.0 (thanks for setting me straight, commenters), but still, good to know about.
Open Settings and go to:
General > Accessibility > Switch Control
Tap Switches to add a new switch. Use a source of Camera, then Left Head Movement and a System setting of Siri. In other words, I want the camera to watch me and when I shake my head to the left, I want the system to bring up Siri.
Now tap back and tap Switch Control to On.
You should see some blue rectangles scanning each item on the screen. Shake your head to the left. Siri should come up.
It might take a bit to get this to work for you, but it is fun to play with and a real boon to people with motor difficulties.
Tap Switch Control to turn it back off. I imagine there’s a bit of a battery suck if you leave it on all the time. I’m interested in your experiences with this.
[Via Business Insider]