https://github.com/kanflo/aaduino

Eagle
An AA sized ISM radio Arduino clone

The AAduino

The AAduino is an wireless Arduino clone the size of an AA battery with Keystone battery terminals rotated 180° to act as positive and negative terminals. It is meant to go inside a 3xAA battery holder creating a very small wireless node.

Powered by an ATMega328p, it is fitted with an RFM69C companion, two DS18B20 temperature sensors and an indicator LED.

Included in this repository is the schematics, bill of material and a sample program to test the hardware.

The accompanying blog post is here.