When friends came home, I let them try UbuntuTouch on my Nexus7. First, I just said « use edges ».
They started and found easily the launcher, then launched gallery, then an image in full screen, and then… lost ! They were stuck on the image, tapping/swapping on the image as much/fast as they could.
I had to tell them « the toolbar is in the bottom edge and there is a back button ».
All this made me think : « what if… there was an emergency mode ? »
Here is a proposal
If you have ideas about other gestures that can be mapped to the « emergency mode », please tell me !