Please explain how I can locate a hidden interrogator and turn it off. Thanks.
You can detect the presence of radio waves using a high-performance digital oscilloscope, such as the R&S RTO Oscilloscope from, Rohde & Schwarz, or a spectrum analyzer, such as the ESA-E Series Economy Spectrum Analyzer, from Agilent. An oscilloscope plots amplitude versus the time of a signal, while a spectrum analyzer plots amplitude versus a signal's frequency.
These devices cost thousands of dollars, and are rather bulky, so if your concern is about, say, an unscrupulous retailer using such a tool to track you via an RFID tag secretly embedded in your shoe, neither device would be a great solution (you would also need to understand a little about the frequencies used by RFID systems to determine if a signal is coming from an RFID reader or some other device).
Montie Design has created a low-cost tool ($20) that can detect ultrahigh-frequency (UHF) radio waves (see RFID Detector Offers Low-Cost Troubleshooting Device). This device will not detect the presence of high-frequency (HF) radio waves, however.
As for deactivating the system, my advice would be to pull the plug, disconnect the coaxial cable to the antennas or take a sledge hammer to it. (Sorry, I am being a little smug.) If the reader is hidden, you would need to create a signal that would jam or confuse it.
In 2003, RSA Security, a provider of digital security products, conceived the idea of a "blocker tag" that could prevent RFID tags within the same reader field from being interrogated. A blocker tag would essentially confuse a reader, thereby preventing it from interrogating any tags within its zone (see RSA Security Designs RFID Blocker). However, I don't think any were actually produced. Hackers could probably cobble together a circuit board with the right electronics to do the job, if they chose to.
—Mark Roberti, Founder and Editor, RFID Journal
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