Last year Google announced that it was working on magnetic nanoparticles that would seek out cancer cells in the bloodstream and report back to a wristband.
Now, the company is also using synthetic skin to develop the technology, reported.
Google employees told The Atlantic that the technology will use light signals to talk to the wristband through the superficial veins on the underside of the wrist.
Shining lights through the skin means factoring in a range of skin types and colours, and so Google's scientists have built fake arms with "the same autofluorescence and biochemical components of real arms."

"It's way weirder to have cancer cells floating through your body that are constantly trying to kill you," said Andrew Conrad, the head of Google's Life Sciences department.