Readers mistaking noise for valid UIDs

Some RFID readers I own think a tag is in the field every once in a while, and report a bogus tag UID. Most notably, the ACM26C (LF - EM4xxx) and the Feitian 502-CL (HF): they’re on 24/7, and every 2 or 3 hours, they beep or flash the read LED, and a random UID gets logged into my system.

I’m assuming they’re picking up random induction noise from somewhere, and when it happens, the noise just happens to be a valid RFID datagram. It’s really not a problem, since the random UID isn’t registered in the system as a valid tag, but it’s kind of annoying.

Has anybody noticed that with other readers?

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rosco this is clearly ghosts


I will see several invalid UID reports a week from my LF (HID Prox3) access control system caused by employees rapidly moving their valid key fob credentials past the door readers. I have never, to my knowledge, had a reader respond to random electromagnetic fluctuations.

I learned rather quickly that presenting my NExT to a door reader while holding a card or fob in the same hand is a coupling game I will never win.

anticollision go brrrrrrr

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I’d also check the security camera footage to see if Deviant Ollam is roaming your halls.

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Seriously, my long range readers are on the floor, and I’m thinking the one that’s acting up is sitting on top of one of the house’s power lines. Either that or its 12V wallwart is crap.

As for the Feitian, it’s never far from my laptop. Hence, it might be getting noise from there. But the ACS122U doesn’t do that at the same location.

Some encoding types have no CRC or parity or error checking of any kind, particularly when it comes to LF stuff… so yeah, it’s possible that noise is creating a recognizable preamble that engages data collection. Even worse, encodings that do have some sort of data integrity checks built in are sometimes ignored by the reader due to hardware settings or firmware that ignores it because they couldn’t be bothered to do the check.