With my phone –it is an iPhone– somewhere very near the bottom of the accessibility/importance chart, is the screen rotation lock. A feature you may need without warning and all of a sudden. Alas, it demands a home button double tap with a swipe and a tap, and another tap. Olympic medals are won with less complicated routines.
I suggest, and I do not know for sure how well this works before it is tried: Toggle the screen rotation lock with a firm double tap to the back of the device.1
It should be feasible from motion sensor data alone, taking directionality of the force into account to discern back taps from screen taps. And should provide a control so ultra-accessible it may be performed in unison with the rotation of the device.
Any home-brew developers willing to test my thesis? Android? Let me hear what you think.
Do not tell me it is a too concealed gesture to comprehend. I mean, shake to undo?! ↩