I have spent the morning searching to no avail, so I figure I will ask here.
I am in the process of making my KBR reader personalized, and I happened to set it on my phone when my phone was locked. It started reading numerous outputs into my computer.
Does anyone know why? I thought when phones locked, the NFC shut off also? It gives a different number when it reads it each time also.
I found the same thing with my note 9 and my s10 5g. They both even when locked with the screen off respond to a arduino nfc reader with varying uid’s (never repeated in almost 1000 tests with the s10)
Hmm, they’re all 8 bytes. Maybe it’s just noise, maybe it’s tossing out random keys to pair with something. I dunno, I’ll look into it. What’s the interval?
EDIT: yeah, it’s random but the last byte is always 8. It must be random UIDs, I was thrown off because they’re usually 7 bytes, but that last one must be a command or filler. I bet it’s for active card emulation mode. You can probably turn it on and off
Android phones have HCE or Host Card Emulation and depending on the reader chip used inside, it may be on by default. Basically when you present your phone to a reader, the chip inside will realize that the phone has been presented to a reader instead of an NFC tag and switch to active-active mode. In this mode, if the reader begins interrogations then the Android phone will present a random ISO14443A compliant UID so the reader can establish a session with the phone… then the phone is expecting the reader to basically be a payment terminal and waits for a common payment AID to be selected. When it doesn’t, or if the session is broken, it cycles and the next read gets a new random UID.