[patcheudor]

"The measurement card has a carefully etched set of traces in the magnetic stripe, (aligning with each of the three data tracks). When a read head contacts the card it bridges a pair of electrical traces and completes a circuit back to the microcontroller."

This seems to me to be a detective control which relies a bit too heavily on obscurity, obscurity which is now blown. Having knowledge of how this works, ATM skimming gangs who's devices might be found by local authorities with this device can now take the active counter-measure of placing a piece of Kapton tape over the read-head.

[kw71]

Or maybe they can monitor the wires on the legitimate read head instead. This was possible on a formerly common fuel dispenser in the USA