Is it possible to use the technology for this purpose?
At one of our events in 2005, ThingMagic gave out a little device that captured energy from a reader and lit up light-emitting diodes (LEDs) to indicate the relative signal strength. A single illuminated LED indicated a weak signal, while all LEDs being lit signified a strong signal. So it is possible to obtain enough energy from a passive ultrahigh-frequency (UHF) reader to light up an LED. In order to use a tag to accomplish this task, the chip must have an output port enabling a user to connect the LED. Some chips have this capability, but many do not.
—Mark Roberti, Founder and Editor, RFID Journal