A growing range of face masks are popping up around the world, but many haven’t proven their effectiveness against COVID-19. A new technique developed at Duke University aims to measure which ones provide the most protection by counting the respiratory droplets they emit during speech. The system is compromised of a black box, a laser, and a cell phone camera. It works by measuring the droplets produced when someone speaks through the mask. The wearer first places their mouth at a hole in the front of the box, and repeats the sentence “Stay healthy, people.” As they talk, the airborne droplets…

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