As title says ,
When you take you key apart ,so you will have 2 bits.
Green pad behind were the button and oppositeside is and small battery and black
Thing ,if I'm selling ecu with transponder is that what is needed in the key,I'm guessing it can be put in another key .
MY03 sti by the way.
Cheers.

 

transponder is the small black thing, almost shaped like a small piece of chocolate.

 

cheers mate.