I have been told in the past that with specialized equipment, passive RFID tags could be read at 1100 feet. This seemed a bit far fetched to me, and sure enough, a quick Google search turned up something closer to 20 or 30 feet. That being said, I know that some of the people who told me this are MUCH smarter (and much better at this) than I am, and the people on the sites I was reading obviously weren't TRYING to get as high a range as possible. Without using something ridiculous like a flatbed truck and some satellite dishes, is it possible (and/or plausible) to read an RFID badge from that far away? If not, how far?
At least 217 feet.
Please keep in mind this is an Ultra High Frequency UHF Gen 2 RFID tag meant for use in item sales, tracking, and inventory. This is not the same RF technology in use by access cards. Those are generally Low Frequency (LF) and have a much longer wavelength, which results in a shorter demonstrated distance of 12-19 inches, although that is much farther than the distance claimed by the access card vendors in the interests of system security. Most door badge readers are designed to require a distance of less than two inches.
Near Field Communications (NFC), found in credit cards, cell phones, and other payment systems, use High Frequency (HF) which falls in-between the two, and they will have a range somewhere between the two. They have an intended operating range of only a few inches, but with an antenna and receiver designed to read them, they may have a much longer eavesdropping range, probably in the 10 foot range. I don't know of specific experiments in distance eavesdropping on credit cards from long ranges; most such attacks have been demonstrated by disguising the reader in a backpack and reading victims' cards through their wallet on a bus or train.
Also, you should not discount specific antenna or receiver technology. If there is value to be had in scanning an RFID tag from across a parking lot (surveillance of a person, that sort of thing) then you can be assured that someone will find a way to abuse it to obtain that value illicitly. They may hide the antenna in a canvas-sided truck to commit their surveillance.