Radio Frequency Identification (RFID): Blocking Reader Scans with Foil

(some say that RFID readers can be blocked by aluminum foil)

Is RFID reliable enough for commercial applications?

Aluminum foil will block the signals emitted by the radio tags that will replace bar-code labels on consumer goods. That is, of course, if you place your tin foil between the radio tag and the device trying to read its signal.

Makers of RFID (or radio frequency identification) tags, along with the retailers and suppliers who plan to use them, are saying the technology they spent millions of dollars developing is too weak to threaten consumer privacy. Metals, plastics and liquids, they say, all block radio signals before they reach RFID reader devices. Apparently, any conductive material can shield the radio signals. There are all kinds of ways to render the tags unreadable and; therefore, useless.

That means Coca-Cola, which eventually wants to put an RFID tag on every can of soda it sells, will have a hard time getting around the metals, plastics, and liquids that block the radio signals from the tags.

This information was revealed at a RFID privacy workshop at an MIT , where privacy advocates squared off with companies planning to replace bar-code labels on their goods with stamp-sized RFID tags. There were several speakers downplaying the threat to consumer privacy posed by the tags, which assign a unique identifying code to each item.

Engineers at the meeting also presented proposals for devices that could deny RFID readers access to a tag's information, or disable the readers by overwhelming them with useless data. They also demonstrated a device that could be used to disable, or "kill," RFID tags at store exits.

What good are RFID tags if they can be blocked?

Many companies, including Wal-Mart, Metro, Tesco, Procter and Gamble and Gillette, have already started tagging items in stores in the United States and Europe; and the companies making RFID tags still plan to help their customers tag every shampoo bottle, soda can, and milk bottle that rolls off the assembly line.

Wal-Mart has been especially cagey about its in-store tests. It has shunned publicity and notified shoppers only vaguely that they are being tracked. Wal-Mart, P&G, and Gillette have also been discovered testing the tags on unwitting consumers outside Tulsa, Oklahoma, and in Brockton, Massachusetts.

There is concern that retailers can use RFID tags to track people in their stores

Civil libertarians have serious concerns about the prospect of retailers using RFID tags to track people in their stores, and—by combining the radio tag data with credit and customer-loyalty-card information—creating detailed profiles of their customers.

Government snoops could also, conceivably, use RFID-based customer profiles in an investigation, and track the radio tags in public places to keep tabs on specified people.

Privacy activists at the workshop also said the companies promoting the new standard for using RFID tags, called the Electronic Product Code, are exaggerating RFID's limitations in order to lessen consumers' privacy concerns.

The companies were accused of putting out two completely different messages. To the public, they are saying the technology is riddled with all of these problems but to each other, they are saying that any day now, they'll be tracking every item.

Wal-Mart and other companies say they are focusing on tagging containers and palettes in their supply chains. They insist that they will not be tagging individual items for many years to come.

It was noted that Gillette has already ordered 500 million RFID tags for its products, and Mario Rivas, executive vice president of Philips Semiconductors, said his company has shipped 1 billion chips for use in the tags. When any company orders that many chips, it is safe to take the situation from theory to reality.

RFID tags are already being used by people who hold their ID badges up to readers to gain access to secure work sites.

RFID tags are already being used by millions of people each day who hold their ID badges up to readers to access secure work sites and board public transportation. Many commuters on U.S. highways breeze past readers that pick up a unique signal from their cars' RFID tags. Many MIT students at the privacy workshop were also surprised to learn that their student ID tags contain RFID transponders.

Reading tags on individual store items will be tricky, however, and spies will find it hard to track items with handheld readers or those mounted in doorways. A sheet of aluminum foil is many times thicker than it needs to be to shield an RFID signal and the signals are also disrupted by human flesh, which is made mostly of salt water; in other words, an RFID tag inside your fist cannot be read.

RFID tag systems also suffer from limited range. The readers—due to FCC tag power limits and design limitations on tag antenna sizes—work at distances up to about 20 meters. In practice, the reading range is much less than that; for example, a laminated anti-static bag would not be readable by even a more potent system.

Excerpts, or clips, for this page came from the article
"Is RFID Technology Easy to Foil?" by Mark Baard, November 18, 2003;
as found in Wired News (

List of Radio Frequency Identification or RFID articles.