Detecting touch using electrical noise on microcontroller pin
An interesting experiment, but there are a few reasons not to rely on this kind of touch-sensing.


A CMOS logic gate can suffer from high shoot-through current when
input voltage hovers somewhere near half-Vdd.
A human antenna boosts    noise input to a gate's input, but random
noise strength varies over    many orders-of-magnitude, making a
reliable design quite difficult.
Chip manufacturers often specify I/O leakage currents very loosely.
Might have only an upper limit of one microamp, but could alsobe sub-nanoamp (and most often is very low).
A gate input sensitive enough to work with a weak noise source is
susceptible to strong nearby noise source. Would you    like your
touch-sensitive keyboard to spit random characters when a    nearby
appliance turns on or off, or when you sweep your charged body-part nearby?


Some manufacturers design input pins for this kind of use, but rely on a locally generated signal source rather than an external noise source.