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RFID credit cards are designed for short-range operation (1 centimeter), and radio fields drop off with the square of the distance. Even as close as 1 meter you're talking about a field 10.000 times weaker. That also means a reader can protect the card being read by adding a low-power jamming signal at 10 centimeters from the reader. Even at low power, it would overpower the passive RFID card everywhere but in the proximity of the reader itself. And that's without a feedback circuit from the jammer to the reader. –

Can there be a small battery powered unit developed to place in a wallet or purse to jam the signal?

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It's possible that a jammer would work, but there are a couple of things to be concerned about. First, jammers that emit RF above a certain power output are illegal across the US and in most of the world.

Next, there are many types of RFID technology in use, and they are all different. You would need to determine which kind of technology you are concerned about protecting.

With NFC technology, as is used in payment cards (you specifically mentioned credit cards), your jammer idea may seriously backfire on you. NFC works by absorbing the RF energy, and using it to power an on-board CPU. The CPU modulates the receiving antenna by applying an alternating high or low load; this switching back and forth causes bits to be detectable by the receiver. The jammer will provide enough RF energy to activate your card, causing it to continually reflect your payment data even when you're not near a reader. It's also entirely possible that a pocket-sized jammer will not have sufficient power to overload the receiver; it may still pick up the NFC reflection from the card even in the presence of a jamming signal. The reader will not discriminate what RF energy source is powering the CPU on your card, it will still be able to read the signal from the reflection. Your jammer might even give your card extra range.

I don't know the legal threshold for jamming, but intentionally interfering with radio reception is virtually always a bad idea. Given you titled this question "RFID safety defense", a jammer is offensive, not defensive, and it would increase your risk of being arrested and prosecuted, which does not increase your safety. Plus, it likely wouldn't work the way you think it might. For defense, you would be much better off shielding your cards, using legal, proven, and cheap shielding technology.

  • Last time I checked ( prior to wifi being available to the general public ) you needed a licence from, the government to transmit outside of a narrow range of frequencies . This should be taken into account. – Damian Nikodem Feb 9 '15 at 17:15
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I believe you're looking for the RFID Guardian project.

The RFID Guardian Project is a project focused upon providing security and privacy in Radio Frequency Identification (RFID) systems. The goals of our project are to:

  • Investigate the security and privacy threats faced by RFID systems
  • Design and implement real solutions against these threats
  • Investigate the associated technological and legal issues

The namesake of our project is the RFID Guardian: a mobile battery-powered device that offers personal RFID security and privacy management. The main focus of our project is to create an industry standard, open source, RFID security product based on our current RFID Guardian. Our group also performed the first-ever research on RFID Malware.

It functions by jamming attempts to read RFID tags in certain scenarios.

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