[CottonBall]

“ The longer you’ve had it, the more time the injected material has had to spread throughout your body, dissipating any material at the injection site itself.”

I wonder how that compares to microchipping. I just assumed whatever they injected into Cooper stayed in him at the same location, for easy reading.

A high tech replacement for number tattoos, for those of us considered domestic terrorists.

[Spirit of Liberty]

I would say the microchip is different; it's a 'thing' that's meant to stay in place. Something like this:

What little I've read (admittedly, I haven't researched it since I'm not getting it) about the injection is that it could be nano materials, which would be more on a cellular level size.