Eh, as someone else mentioned the soft switch, you could very easily make this teardown resistant by putting the covert power rail on an inner layer of the pcb with the switching transistor out of the way connected to vias. It’s not teardown-proof, but wouldn’t be obvious with a trivial inspection.
Perhaps but this would also remove any pretense of deniability from the manufacturer. If discovered it would just show that they went to great lengths (extra engineering effort to implement and hide) which could only be explained by the conscious decision to make it a back door and bypass it later in software.
So the issue would no longer be one of ignorance (no button) but of premeditation (button with hidden bypass).
