Small radio kits
http://www.electronickits.com/kit/complete/complete.htm
Other possibilities:
Food completes the circuit.
By Justin Meyers at Wonder How To
USB wifi adapter plus parabolic vegetable strainer
At wonderhowto.com
http://mods-n-hacks.wonderhowto.com/how-to/make-wi-fi-extender-from-asian-parabolic-cookware-77212/
Inexpensive programmable DSP chip
Catalog of free open source example programs:
http://www.spinsemi.com/programs.php
Underwater ultrasonic mesh networks by Subnero
from docsity.com
By Charles Q. Choi in Popular Mechanics