A Compact, Wireless, Self-Powered Pushbutton Controller” by Joseph A. Paradiso and Mark Feldmeier, 2006:

Very important reference, as it shows the first example of an RFID tag with enhanced functionality. It transfers the energy of pushing a button to power a RFID circiut and sends back an ID across an entire floor of an building. Talks about the technological realisation, most of the time.