LF Phone Unlock 📱 - Failed - Kind of

A quick and dirty project description

So my plan was to build an LF RFID reader into my phone case, for login and password etc.
With a T5577 chip, this can be changed easily and as frequently as I choose, especially in the situation of a password compromise.

I like a low profile phone case, so I needed a small form factor reader, I chose this

~ USD $8
They make an HF version and an LF version, that look identical
The also come with a micro and Type C adapter

The plan was something like this ( or LF Board and antenna side by side above the NFC antenna if it affected performance )
I wanted to keep clear seperation between the HF and LF antennas, for when I was using my NExT.

I generally use Wireless charging so I was happy to dedicate my charging port to this added functionality

A ribbon cable and low profile Type C plug was the plan for this.

and connect that to the internals by removing and replacing the Readers Type A

I carry a spare T5577 card in my case, So I would have to remove this

The layout was to look something like this ( As per plan above )

A couple of things to note

Results of some quick testing; it only reads EM410X
I only tested further with HID Prox, and FDX-B that didn’t work
The antenna is an OK size, but testing with the xFD showed it was optimal on the long sides only

( brighter in person )

It reads an xSeries ( in EM410X ) though my case


  • There is constant power to the reader

This is both a good thing, and a bad thing
You can wake your phone with an implant
You can set your pin to login immediately
( 2 swipes and you are in )

Tested with fob on video, but it also works with implant

This constant power usage, was a power sacrifice I wasn’t willing to make,
for this reason, I decided not to continue with the build.

I did consider embedding a power switch to the case,

but that removes the fluidity of the build I was going for

There is still another option for those that may want to use it, Its not elegant but it does work…
as per the video, just carry the reader with you.

Anyway, I said it would be quick and dirty and hope it was of some interest to somebody


Of course if you have a giant battery with phone functionality, it might be a viable build

I have a USB power meter, I will measure the draw when dig it out

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I’m getting a librem 5 phone eventually (probably 2nd Qtr of 2022) so ill have to make something like this.

that’s built into it afaik. I’ve got the same one and it only reads em4100 tk4100 and smc4100

try an em4305 if you have one on you, they’re said to work (source: RFID Tag Reader Pendrive USB HD-RD60)

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Thanks for those, I have pretty much shelved it at the moment, I just grabbed the cards I had at hand to test. But good to know if I have another play with it later