From what I can find on the Internet about active RFID systems, it seems the reader sends out a signal at a certain frequency and if a transponder tag that operates at the same frequency is within range, it will activate and send its signal back to the reader. Quoting from the site I found this:
In a system that uses an active transponder tag, the reader (like passive systems) will send a signal first, and then the active transponder will send a signal back with the relevant information. (Source)
I understand this concept at a very basic level but I am wondering why transponders that operate at 2.4GHz are not activated by being within range of a wireless router? If they respond to RF waves at that frequency wouldn't they be activated and send out a signal, albeit one that would just get ignored?
I have no background in this and am just starting to learn about RFID so if anything I said is fundamentally flawed or unclear I apologize.
Best Answer
The tag is not activated by just any RF signal, even one transmitting on the tag's preassigned frequency. The tag receives an RF signal that has certain information encoded in it. If the RF frequency is within the tag's preassigned frequency, and the received signal contains a code that matches the tag's preassigned "turn on" code, then the tag will in turn transmit it's data.
The chances that a random wifi signal will match both the frequency and codeword requirements of any given tag are vanishingly small. By design.