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Was doing a design that requires light detection. Blocking light with a hand resulted in no light obstruction. Because some parts of a hand conduct some light frequencies.
A few Japanese electronic companies make biological security detection equipment for ATMs. One view the entire palm. Another views fingers. Each looks at veins. Because veins obstruct many light frequencies that easily pass through other parts of a hand.
Chop the hand off. Then veins are no longer useful for logging into an ATM.
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