Spark 2 vs xNT vs xSIID

There has been some confusion with regard to the features and benefits of the Spark 2, and other more traditional NFC chips like the NExT, xNT, or xSIID. This post will attempt to explain some of the differences.


The Spark 2 (NTAG413/424)

The Spark 2 has an NTAG413/424 chip inside and is a cryptographically authenticatable RFID transponder, meant to be used primarily with the VivoKey service platform for secure identity applications and service offerings.

Because it operates on 13.56MHz and is ISO14443A compliant, it can also communicate it’s unique ID (UID) to compatible readers just like any other ISO14443A transponder. This means some access control systems may be able to use the Spark 2 as an access token, if properly enrolled in the system. Some devices that might read other ISO14443A transponders may not respond to the Spark 2 however, which is due to firmware programming inside the device either being written to only support a specific type of ISO14443A transponder, or being deficient in some way so as to only support specific transponder types and excluding other ISO14443A compliant transponders.

The Spark 2 is also NFC Type 4 compliant, meaning it can be communicated with using NFC standard protocol commands. Typically NFC transponders can carry small pieces of information like a URL or a vCard digital business card or even simple plain text data inside what’s called an NDEF record. The NDEF record is a specific format of data that is stored inside user writable memory of the chip. The Spark 2 has no user writable memory, but it does have a unique VivoKey platform URL pre-written to the memory space which is locked as read-only. When scanned by a smartphone using NFC, the VivoKey platform determines what should happen… either display some information or redirect to another URL you’ve specified through the VivoKey mobile app. In this way you can use the Spark 2 as a basic data sharing NFC chip, similar to the NExT or xNT.

NExT / xNT (NTAG216)

The NExT and xNT both have an NTAG216 chip inside. This type of chip is commonly used with simple NFC applications meant to be read by smartphones such as SmartPoster type applications.

In short, this NFC chip is meant to carry simple NFC data and convey it to a smartphone or other NFC compliant reader without much fuss or security involved. As an implant, it can function as a simple ISO14443A RFID transponder with certain compatible access control systems, as well as NFC applications like sharing a URL or vCard digital business card with anyone who scans the chip with their phone.

The user memory area can be written and re-written many times using smartphone apps like TagWriter or NFC Tools, and even supports a simple (not actually very secure) password protection feature.

Like the Spark 2, the NTAG216 in the NExT and xNT is also ISO14443A RFID so it can be used with certain compatible access control systems, if properly enrolled.


The xSIID contains an NTAG I2C chip which enables the addition of a colored LED which lights up when the chip is scanned. For all intents and purposes, this chip works exactly like the NTAG216 chip in the NExT and xNT. It is 13.56MHz and ISO14443A, as well as NFC Type 2 compliant. The only major differences are;

• The xSIID contains an LED
• The xSIID memory is 2kB, but split

The user memory of the NTAG I2C is split into two sectors. The first sector is what is used for NDEF data (NFC applications) like sharing URLs or vCard digital business cards. This sector is exactly the same capacity and functions exactly the same way as the NTAG216 chip in the NExT and xNT implants. In this way, there is no functional difference between the xNT or the xSIID when it comes to RFID or NFC function. The LED inside the xSIID is the only real difference.

The second sector of the NTAG I2C chip inside the xSIID contains an additional 1kB of memory, but it is only accessible by using special applications that can read and write directly to it. The reason for this limitation has to do with problems with smartphones and the NFC standard, not necessarily the chip itself.