Detective Vance investigated a break-in at a high-tech laboratory. The thief bypassed the electronic retinal scanner by holding a severed eye up to the lens. Vance examined the security log and immediately knew the retinal scan was fake. What proved it?
A retinal scanner requires a living human's blood flow and pupil dilation, which a detached eye lacks instantly upon death.
Biometric retinal scanners check for vascular pulse and reflex dilation. A severed eye lacks blood pressure and nervous response, causing the scanner to automatically reject it.
About this riddle
Detective riddles are tiny mysteries. Look for the detail in the story that does not fit; it is usually the clue that solves the case.
Difficulty: Medium. More like this: Detective riddles with answers or try Truth & Lie Island for a different kind of puzzle.
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