A hidden transmitter, or fox as it is sometimes called, is used by amateur radio operators for sport. Somebody hides a fox, and participants use different methods to find it. This is for practice for when there is an illegal transmitter nearby. Then the "hams" know what they are doing when tracking it down.
The transmitter usually transmits a long tone followed by a fcc granted call sign in morse code. The club I am a member of needed one of these, so I sat down and started designing it. I based it around an arduino, though this could be ported to many different microcontrollers.
Step 1: How The Code Works
EDIT 12/7/13: In the original code, you must insert the morse for the call sign to be transmitted manually. In the updated (albeit messy, apologies) code, you just need to input the call and any other text in the string Text. For the program to transmit the easterEgg string instead, you must hold pin 10 high at reset. This is what qualifies the project for Hackaday's contest.