Whilst talking nonsense at work - for a change, my student and I realised that an input device for computer tablets and other kinds of small devices is readily available...in the shape of teeth.
A normal human has 32 teeth easily covering the Latin Alphabet with only a modicum of multiplexing. For
example the lower case can come from the lower set of teeth and upper case from...well the upper set. See how easy it is to remember?
The device has two sets of braces, one for upper and lower, and small stylus. A modest electrical current* runs between the two when they are in contact.
As an added bonus, two sets of false teeth can be rigged into one of ergonomic keyboards, letting old couples join in the technology fest that is the internet.
As an added-added bonus, you can also use the stylus to winkle out stubborn bits of cabbage and whatnot, in fact the initial marketing slogan was the (goodbye) Cabbage (see the) Difference Engine.
I rest my case, and my incisors.
*At little as 13 amps should do the trick.