What does it do ? Well , it generates a sound similar to the sound that a water drop makes when it's dropped in a bucket or any other plastic object.
You can adjust the frequency of the drops by rotating a variable resistor , and it works with voltages between 6v and 3v .
Step 1: Parts
So , what you need is :
--1 General Purpose NPN Transistor (prefferably 2N3904)
--1 General Purpose PNP Transistor (prefferably 2N3906)
--1 10 Microfarad Electrolytic Capacitor
--1 Battery holder
--1 Variable resistor (100 K ohm)
--Your favorite soldering tool