The 4093 or any other NAND gate can be used for the very sensitive configuration of a R-S fIip-flop triggered by the touch of the finger in two sensors. The circuit is shown here. The sensitivity depends on R1 and R2. The Iarger these resistors are, the higher the sensitivity. The sensors are two small metal plates that can be touched at the same time with the fingers.
Touch Triggered Flip Flop
