Since I have chipped animals I know a tad about those chips. They make them as small as possible for the convenience of the animal, still they have not made them so small it is painless to inject them unfortunately.

They compare the chip size with a grain of rice, but I'd say it is at least twice as big. A chip this size you can fit basic information, like a string of data. It cannot hold massive amounts of information. Another thing that does not fit with that size is a power source. That means, you cannot read any data off the chip at a long distance. You have to send an electric pulse to read the chip. The chip reader does two things, it provides the chip with enough power to have it "send" the data, and it retrieves and reads the data also. With the weak power of the reader it is only possible to read data at very short distances, it just takes a few inches off and you will miss the chip.

The chip is encased in silicate which looks like plastic. The idea is for the chip to stay put, so the body will not shove it about or out. Despite this, sometimes chips travels a bit in the animal but I have never seen one coming out.