There has been a fair amount of hype about touchscreen smudge attacks (ie potential attacks). I’m pretty sure this has been made up by a journalist but in any case the problem is easily fixed by routinely changing the spatial order of the symbols to be touched.
A more serious problem occurs with existing, fixed key pads in very high security applications.
If eg a bank employee is under surveillance, by criminals using a super-sensitive thermal camera, his or her entry sequence will leave traces on the pad, with the residual temperature pattern varying according to the order in which these have been pressed.
Today’s invention is to supply each such installed pad with an automatically-activated hot air gun which can instantly eliminate any such thermal distribution.