When nearly 30 years ago Dr. Jacob Fraden invented an ear thermometer working on this second principle, the infrared light sensor was so large that he needed a narrow gold-plated reflective tube to channel the light from the ear drum to the sensor.

FORBES: Body temperature.

It works by combining a 3D sensor with a projector that emits an invisible, infrared light in a complex pattern.

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It also uses an accelerometer and light sensors to snap an image when a person enters a new environment, and an infrared sensor to take one when it detects the body heat of a person in front of the wearer.

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