NEW YORK (CBSNewYork) — By now it is quite clear that COVID-19 is a very different kind of viral infection.

It causes a wide range of health problems, from strokes, heart attacks and multiple organ failure, to the loss of taste and smell. But by far the deadliest of the pathologies seen is what’s come to be known as COVID pneumonia, when the lungs fill with fluid and the patient can’t take in oxygen or get rid of carbon dioxide, CBS2’s Dr. Max Gomez reported Wednesday.

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What’s odd about this pneumonia is that patients often suffer a kind of “silent hypoxia.” They don’t feel their lack of oxygen and by the time they do, their blood-oxygen levels have dropped to near lethal levels and they have full-blown pneumonia.

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But there is a simple device that can detect this drop in blood-oxygen well before you start getting out of breath. It’s a fingertip gadget called a pulse oximeter. Simply place it on the finger, press the “On” button and in a few seconds, you get your heart rate, that’s your pulse, and more importantly, your blood-oxygen percentage.

CORONAVIRUS: NY Health Dept. | NY Call 1-(888)-364-3065 | NYC Health Dept. | NYC Call 311, Text COVID to 692692 | NJ COVID-19 Info Hub | NJ Call 1-(800)-222-1222 or 211, Text NJCOVID to 898211 | CT Health Dept. | CT Call 211 | Centers for Disease Control and Prevention

You don’t need a prescription, and while pharmacies may be sold out, they are readily available online. They are not cheap, but they can be shared with a little disinfection.

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So if you have a cough, fever, or fatigue, think of an oximeter as a canary in the coal mine — if you get an early warning of dropping blood-oxygen, doctors can intervene before you need to be put on a ventilator.