How does ergodex keyboard works?

Hi, I saw this project, there's also a working video presentation, and I can not understand how it works. So I got very interested to implement such behaviour with arduino somehow, just with simple buttons.
So my main problem is that I do not understand how it transforms remote click signal from any button. Its clear that there is some kind of transmitter in each button with specific signal, and the in the surface its placed some kind of receiver. The question is how can it be implemented? This transmitter in button should have no power, so it should somehow transform kinetic energy from pushing down button to digital signal somehow? All I can guess from physics is some form of piezo electricity (and I\m afraid my guess is just too bad)... Or there's another way in which it somehow receives energy from this surface it placed on, is it possible? Or its much more simple, and there's a little replacing battery as in hand watch, but again, how signal translation can be established? Some kind of IR, like in tv remote?

If anyone can explain to me how can this work, or maybe some projects with such demonstration, please help. thanks.

Oh, I already got it - its some kind of RFID's in keyboard buttons.