Aluminum Foil Does Not Stop RFID

There have been important concerns raised about plans to place radio frequency identification technology in items such as U.S. passports. There are concerns about the possibility for identity thieves to obtain personal information about people from such RFID-enabled items, and there are concerns that these items could help to create a "surveillance society" by enabling the creation of records of people's movements between different physical locations. As such, I was not pleased when I received a new student ID card from my university that contained RFID technology.

I decided that I would try to defeat the RFID transmission of the card. After a bit of googling, there seemed to be a consensus online that wrapping an item in aluminum foil (or tin foil) would block the RFID transmission. So, I wrapped my student ID card as suggested.

Then, I took my ID card to the entrance of a dorm on campus where there was an RFID reader. Even with my card wrapped in Wegman's brand aluminum foil (with aluminum covering the entire surface area of the card), the reader still beeped that it could detect my card when I moved my wallet close to the reader. The apparent consensus that I had found online was wrong.

The aluminum foil did, however, help with preventing the card from transmitting. Without the aluminum foil, my card was detected by the reader at a distance of about a foot and a half. With the aluminum foil, the card was not detected until it was about two inches away.

This does provide evidence that aluminum foil can be used to substantially hinder RFID, but the important note that I wish to make here is that the apparent consensus online about aluminum foil actually blocking RFID should not be believed.

For my purposes, after talking with a representative from my university about the actual data that is transmitted by my card (which is encrypted and which includes no personal information), I decided that limiting the range of transmission to two inches would be sufficient for me.

Update 10.15.07:

I discovered that this page is linked to by the following page on the website for the RFID Shield. There it is reported that in a similar test to mine, the aluminum-based RFID Shield was 100% effective in blocking RFID transmission.

I contacted RFID Shield and offered to test their product in the exact same way that I had tested aluminum foil. In what is probably a good sign of business ethics, they agreed and sent me their product for testing.

I went back to the same reader that I had tested the foil on and used the same ID card that I had used then. Again, with the card unshielded, it was detected about a foot and a half away from the reader. I then put the card in the shield and when I placed it very close to the reader... yes, it was again detected.

I took detailed measurements this time of when the card was detected. With the label of the shield facing out, the card was detected at a distance of about 1 1/2 inches. With the label of the shield facing in, the card was detected at a distance of about 1 inch.

If I held the card perpendicular to the reader, it was much harder for the reader to detect it. I could, in fact, touch all four sides of the card to the reader without any detection. If, however, I moved the card around a little bit, with it still perpendicular and still touching the reader, eventually the reader would detect it.

I made a video with my digital camera of me slowly bringing the card close to the reader, so you could see when it is detected. Download the video here. If you are having trouble seeing the video, you most likely need the XviD codec.

Comparing my test to the one discussed on the RFID Shield page, you can note from the pictures that the reader I used was much larger than the one used in their test. Moreover, they report non-shielded reading at four to six inches, while for me it was at about a foot and a half. It would appear then that the reason for our different results is a difference in the strength of the readers.

I would maintain that my original conclusion still holds: aluminum foil does not block RFID but does seriously inhibit it. That is, the RFID Shield does not completely prevent all RFID transmission but would appear to limit reading to only strong readers at very close distances.

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