It’s surprisingly hard to get representative data on the touch screen resolution of smartphones -eg the just-detectable change in separation for fingers placed at opposite sides of a screen.
A figure of a couple of mm seems plausible, with today’s capacitative technology.
Today’s invention attempts to use the sensitivity of smartphone screens to guard them against damage, when you bend with your phone in your hip pocket
First, slide a sheet of inextensible plastic, fitted with two rubber prongs (red), into your hip pocket (blue), before inserting your phone (clear) as shown.
When you bend, the prongs get closer, a fact which is registered by the touchscreen. Too much bending and the phone itself would alert the user with a buzz or beep.
This could also be used as a tool to detect repeated stressing of one’s back eg when sitting.