What’s the Deal With Pulse Oximeters?

Here’s what to know about devices that can measure blood oxygen saturation

Pulse oximeters measure the percentage of your red blood cells that are carrying oxygen by beaming different wavelengths of light into your finger after it’s clipped on. Photo: Smith Collection/Gado/Getty Images

People showing up at the ER with suspected Covid-19 tend to have an especially concerning symptom, explained emergency room physician Dr. Richard Levitan in the New York Times this month: Pneumonia caused by Covid-19 comes with dangerously low oxygen levels that sometimes go…