The first version of the device was a transistor and some copper tape connected to an Arduino Pro Micro. 

It was really crude but got the job done, below is an image of the device and schematic diagram

I was using a BC547 NPN Transistor. The 100k resistor is a stand in for my lips which bridged the collector with the base which pulled the logic line connected to Arduino LOW. This then send the emoji key presses over USB to my computer

The prototype had the 5v line and Transistor Base connected to 2 separate strips of copper tape that were connected via your lips when ever you kissed it.