What to buy for remote start button?

Somewhere in the blurb I saw that some button on some earpiece will remote start the iStopMotion for Ipad.
Can’t find the reference again, and Ipad’s don’t come with an earpiece, please tell what I have to buy to get this functionality?

hello?

Hello! And sorry for the late reply: Its the Apple Earphone http://store.apple.com/us/product/MB770G/B . Push the center button to capture a frame.