RFID distances

February 17, 2005 8:38 PM

RFID proponents always point out that its effective distance is only a couple of meters at best and therefore couldn’t pose a significant privacy concern in the future if used on people. However, wouldn’t that effective distance be much larger if more powerful transceivers were used than current models?
posted by trinarian to technology (17 comments total)

what are the links for hacking rfid?
posted by specialk420 at 9:01 PM on February 17, 2005

From what I understand ...

Long-range, high-frequency receivers have a range of 20-25 ft. And some will allegedly go 100 ft. But of course, "... the higher
performance of high-frequency RFID systems incurs higher system costs."

Realistically, it's not an issue of privacy or rights that will determine RFID's mainstream entrance to market; rather it is one of when it becomes cheaper for an industry/company to to manage/track their assets via RFID than by any other means. And China is leading the way.
posted by fourstar at 9:36 PM on February 17, 2005

I guess what I'm getting at is what if RFID were installed on something like a drivers license/ID card... could police effectively do occasional "sweeps" and database peoples locations within a certain (large) radius? Even if cost 10x more for a different chip, we're still talking under $1 a unit which could be passed down to the buyer/citizen pretty easily.
posted by trinarian at 9:56 PM on February 17, 2005

The House of Reps passed the REAL ID Act last week which includes a provision that would allow (if not mandate) including RFID on all driver licenses.

There is however bipartisian opposition. It is unlikely that it will pass through the Senate.

So I guess you're safe. At least in the short-term future.
posted by fourstar at 10:16 PM on February 17, 2005

This technology works great for cars passing through the 407 toll road. Working distance is at least 25 ft. maybe 100 ft.
posted by shepd at 11:04 PM on February 17, 2005

Many RFID tags are powered using induction from an external source (built into the reader). In this case, it doesn't matter how powerful your transceiver is, the chip won't respond if it's not getting power locally.

You could try to snoop on a transaction between an RFID and a reader, but it should be encrypted.
posted by krisjohn at 11:47 PM on February 17, 2005

I guess what I'm getting at is what if RFID were installed on something like a drivers license/ID card... could police effectively do occasional "sweeps" and database peoples locations within a certain (large) radius?

Yes, IF they could have two to three receivers at a known distance from one another and tied together with wire. The farther the distance or the higher resolution, the longer the distance. If you want to locate something with very decent accuracy, you'd have to have three receivers. Basically, you need to triangulate.

However, RFID is very useful for 'gateway' sensors -- for instance, knowing that you entered a particular building and when, and when you exited a particular building. Nothing that isn't already handled with cameras, for instance...

IANAL, it's still not anything that could be proven in a court of law (although it could be used as probable cause for an arrest) because someone else could've stolen or spoofed your ID code and since the police aren't verifying it's actually you that has that particular card that they're sensing, they're just proving that a card with your card's ID code was in a particular area/location at a particular time... all of the privacy concerns about RFID tags are pretty much groundless panic-attacks.
posted by SpecialK at 12:02 AM on February 18, 2005

I was under the impression RFID chips merely reflect back signals sent to it with a slight variation (the data) without needing any real power of it's own.

How much does RFID resemble IFF on military aircraft?
posted by trinarian at 2:53 AM on February 18, 2005

One important limit to functional range is noise from other RFIDs in the same area. You can read one or two signals easily enough, but it would be pretty hard (impossible?) to reliably distinguish between several hundred RFIDs all responding at the same time.

krisjohn points out that some (many? I have no idea about the proportion) RFIDs can be powered by induction. For anyone who doesn't know what that means - think of it like a transformer, the reader contains the primary and the RFID is the secondary (anyone with a rechargeable toothbrush can see this in action in their bathroom). This means you can put powered electronics into the tag, which gives you much more capability. Induction powered devices work over very limited range because magnetic field strength falls very quickly over distance. Here are a couple of non technical articles addressing the field strength roll off: Near-field magnetic communication and Physics of EMF. (the first says 1/r^6 referring to energy, the second says 1/r^3 referring to field strength. the math escapes me at the moment, but at least the two are consistent)
posted by Chuckles at 8:07 AM on February 18, 2005

I had looked into this a while ago wondering what the feasibility of recording the people around me carrying metro cards would be. Something like walking around with a RFID receiver on my PDA or something that would ping whenever I was near someone I had been near before (geek art).
But the range on those cards is really in the inches. I had thought that the distance limitation might have had something to do with the power of the transmitter (reader), more power more distance, right? Nope. In RFID cards like that they actually transmit data by modulating a magnetic field put of by the reader (subway turnstile), where the devices like the once you have in your car for paying highway tolls actually receive power from a radio frequency and transmit data back out on a radio frequency. There are many different types of RFID to the point where hearing FUD about invasion often gets blown out of proportion.
posted by dirtylittlemonkey at 8:34 AM on February 18, 2005

Even if they had super-duper receiver, you could always put the card in one of those signal-blocking bags, like they give you with the tollbooth transponders.
posted by smackfu at 8:39 AM on February 18, 2005

I've worked on passive RFID products and one thing we consistently saw was that in order to get better range in the reader was bigger coils, more power in the reader and alignment of the coils. If the coils aren't well aligned, you don't get a good read at distance. Tighter coils (like the Tiris/Mobil Speedpass formfactor) are less susceptible to alignment issues at close range, but the range is still limited. Different systems use poker chip, pog, or card form factor. These can have a greater read distance, but need more careful alignment.
posted by plinth at 9:01 AM on February 18, 2005

The minute I get my first RFID'd ID card is the minute I'll be ordering one of these faraday cage bags.
posted by Zed_Lopez at 9:25 AM on February 18, 2005

Working for a company that uses RFID technology in a transport system, I just don't get the worry about being able to locate and track you down. It's all about statistics. If other companies are the same as us, we just don't care about where you are and what you are up to! All we need the data for is primarily customer service, making sure you are charged the correct amount for your travel and looking at transit flow. The only time we look specifically at customer's personal data is when they call us. As for police requests, here in the UK, they have to provide us with a Data Protection request and that will only be for serious issues. We don't give out info 'willy nilly' and you have the Data Protection Act to protect you. Besides, if you're worried about the tracking you down part, as fellow MeFites have mentioned, with the RFID we use, you can only check on usage and location when the card is physically scanned and needs to make that connection with the powered reader. Don't forget - if you have a mobile phone you can be traced anyway!
posted by floanna at 10:35 AM on February 18, 2005

Floanna, the concern is more about rogue readers, since any random person can read the RFID that your company requires.
posted by smackfu at 11:11 AM on February 18, 2005

I'm not an expert, but it seems to me that no matter how powerful the signal that is sent to an RFID tag, the key variable is the strength of the signal that the RFID tag sends back. And the strength of that signal is (I'm guessing) limited by the circuitry in the RFID tag. In other words, if you send a signal that is 10 times stronger than normal to an RFID tag, that won't change the strength of the signal that the RFID tag sends back, assuming that a normal signal provides full power for the tag.

So, to answer the question, no, a powerful transceiver wouldn't allow long-distance reading of short-range RFID tags (if the suppositions in the previous paragraph are true.)
posted by WestCoaster at 11:24 AM on February 18, 2005

West Coaster, I think that really is completely wrong. There have been some links posted that are far more authoritative than I am, but I have never let that stop me...

I believe there are tags which are essentially just highly tuned antennas. The reader broadcasts a frequency sweep and when it see the right type of reflection it knows that the tag is in the vicinity. (If this isn't used I declare a patent, anybody have venture capital funding?)

Tags with inductively coupled active electronics would suffer from the limits you say, of course.

floanna, we are getting off topic, but I can't resist. The problem is that this type of information makes it too easy for authorities to enforce arbitrary stupid laws. It also yields a lot of false positives ("you are Arab and you drove the same route as a known terrorist, you must be one of them too"). I'm sure I can think of other problems...
posted by Chuckles at 7:28 PM on February 18, 2005