This circuit allows many uses :
It runs from battery. There is a CR2032 holder on bottom, but it can also be powered with 2xAA batteries, on a separate header.
You can also directly provide the 3.3V on another header.
There is 2 inputs : both have pull-ups pads to solder a resistor, but are optionnal (if you prefer to use atmega internal resistor).
The power stage uses a MAX1724EZK33+, which converts input voltage from 0.8V to 3.3V to fixed output of 3.3V.
The radio module used is a RFM69(HW).
Circuit size is 50x30mm, which is about the same size of 2xAA batteries. You can the place it almost everywhere !