Chip

From Live Cinema Research

Maybe just like a small flash memory card or SIM card. If they're a standard chip they would have a distinctive shape to avoid it being used in the wrong places, or being mis-identified, but if Ping was making them herself, there would be no need for this. Maybe she is re-using memory chips from a standard source, though.

Would be small in size - no need to be large, and if it's small it's easy to carry lots of them. Maybe it has a small LCD display on the side to display a name that Ping gives it, to make the loop identifiable from the outside of the chip.

Perhaps the chip has some sort of adhesive on it to stick it to the wall, or it is pressed into the wet 'paint' that Ping sprays on.