I first considered using the Adafruit Feather Bluefruit, but it was out of stock and I already had an Arduino Micro handy. Over on the Adafruit forums, [richarduk] managed to get his hat working with the Feather, AND with more than the 20 character limit.
Why a hat? I volunteer for Destination Imagination, and during
competitions Appraisers are encouraged to wear a creative hat. As
usual, I first came up with a project I wanted to try, and later figured
out how to strap it to a hat. I left as much electronics exposed as
possible because DI is a creative problem solving competition and the
kids typically want to learn the how and why of my hat. http://destinationimagination.org/