Have you had any luck yet with a read?
Ahh, Say no more
SO are you aware, that the xSIID has 2 writable sectors ( 0 and 1 ), 0 the first 1k ~ 888 bytes works like the NTAG216 ( such as the xNT and NExT etc ) and you can write to it with TgWriter / NFC Tools etc, the other sector (1) you will need to use NFC shell to write to the chip.
Sounds interesting
Have you seen Roscos
“SO are you aware, that the xSIID has 2 writable sectors”
Yes, spent a lot of time today setting it up on ubuntu, seems it works …
thanks for the theremin link, didnt know this project … perfect!
@krtrttx Maybe you could try to extend the range on your phone? 
https://forum.dangerousthings.com/t/extended-nfc-range-on-phone-scan-a-flexnext-through-hand/7453
Edit: ok, so I had to try this myself.
I have a Sony Xperia 1.the NFC antenna works good, so I initially don’t have a problem, as long as I orient the implant correctly
In any case, I ripped apart a normal tag and placed the coil over my phone, and boy did that make a difference.
I no longer need to “twist” my glassies to get a good read.
Recommended!
Hrmm… I see a 3d-printed phonecase with integrated coil project coming up. 
Yet another edit:
So on my Sony Xperia 1,the range became noticeable better, placing a coil on top.
… But the same procedure on a Samsung galaxy s10 didn’t improve at all.
The antenna designs are vastly different, so I assume th xperia has a more ‘concentrated’ beam, whilst the s10 has a broader coverage but a bit weaker overall signal 
In any case, worth trying it out at least.
It looks like the coil has no chip or capacitor or anything, just two open leads… basically the coil is not connected to anything… is that the case?
That is correct. I removed the chip from the coil so it’s simply a coil over the existing phone antenna.
Edit: It seems the effect is purely psychological 
I tried reading a standard magic card, and managed to get a proper read from about 28mm both with and without the coil. - no difference
I then tried using the xfd, and had high hopes I could see a difference, as I got a good light all around the coil.
… But got the same result without the coil. (I think the NFC antenna is about the same size, only square)
I also tried to see if I could get any voltage difference on the proxmark, or increase in range on the xfd, but nothing.
The feel of increased range is simply because I now have a visual representation of where to place my implant, and so I place it correctly on the phone every time 
Good on you for further testing. It might improve things if you connected a proper capacitor tuned with that coil inductance to resonate at 13.56mhz
