These devices can monitor coronavirus symptoms at home — but do you need one?

Place a pulse oximeter on your fingertip, and it reads your body's oxygen levels. Here's what experts say about using one for the coronavirus.

For many individuals who develop symptoms of the coronavirus, it's better to stay home than seek health care in person. But when you have a disease with so many unknowns, not having a nurse or doctor to monitor your condition can be nerve-wracking.

As "Watch What Happens Live" host Andy Cohen discovered, the self-isolation you should practice if you're sick, as well as the illness itself, are enough to drive you "crazy." Cohen, 51, who has asthma, tested positive for COVID-19 almost two weeks ago.

On Tuesday morning, he chatted with TODAY anchors Savannah Guthrie and Hoda Kotb about how he coped. Because of his underlying condition, he said his experience was "a little scary" before talking about a device his doctor recommended to help him track the severity of his symptoms.

"(It's) called a pulse oximeter," the Bravo star recalled. "That’s one of those little devices. You can get them at drug stores, and you stick your finger in it to take your pulse. But what it also does is measure the level of oxygen that’s going to your lungs."

He added: "There were some nights where I thought, this doesn’t feel right, and I was able to use this pulse oximeter and see what the reading was. My doctor said, 'If it goes below (a certain) reading, give us a call and then we’ll talk.'"

What exactly is a pulse oximeter?

It's an electronic hand-held device that measures the saturation of oxygen carried in a person's red blood cells, according to the American Lung Association. You usually attach it to your fingertip to get a reading.

"It calculates the oxygen level based on how red the blood is," Dr. Eric Cioe-Pena, an emergency medicine physician at Northwell Health in New York City, told TODAY. He added that it can detect changes in oxygen saturation "pretty readily."

"That's useful because in COVID-19, one of the things we're seeing is people with severe pneumonias who come to the hospital have low oxygen levels," Cioe-Pena said. "One of the ways you can monitor high-risk patients is by asking to get a pulse oximeter they can use at home."

The device helps patients when they're feeling short of breath answer the question, "Is this something that's serious and I need to go to the hospital, or this something I can wait and see about?" Cioe-Pena explained. A reading below 90 merits contacting your doctor "sooner rather than later," he added.

Do you need a pulse oximeter?

More than likely, the answer is no, according to Cioe-Pena.

"Average American families with no medical problems, I would not ask you to buy these," he said. "Like everything that’s being made right now for medicine, we don’t have enough of them ... We want these to be for high-risk patients, for people that are likely to develop COVID-19 pneumonias."

This high-risk group comprises primarily older individuals and those with underlying health conditions.

If you have asthma like Cohen does, you may or may not need a pulse ox.

As Cioe-Pena explained, people who "have never, ever been hospitalized for asthma ... probably don't need one." But for asthmatics who visit the emergency room multiple times a year or who often develop bronchitis or pneumonia from a cold, then yes, there are benefits.

"Those are high-risk people," he added. "Asthmatics who have real problems with their ability to oxygenate in general ... should discuss it with (their) doctor."

If you need one, what kind of pulse oximeter should you buy?

If you do meet the criteria for someone who would benefit from a pulse oximeter, talk to your health care provider before purchasing one.

Why? "The pulse ox is really only good when you've got someone who can render therapy after," Cioe-Pena said, stressing that right now these devices are most useful in hospitals.

Once you and your doctor agree on a course of action, you should buy one that's approved by the Food and Drug Administration. "We know that at least some of (these) have been tested to make sure they're accurate," Cioe-Pena said. Most of these devices cost around $20-$60.

Ultimately, when assessing whether to buy a pulse oximeter, you should think about whether someone else might benefit from it more than you.

"Over-purchasing and hoarding of supplies is what makes them not available for people who need them acutely," Cioe-Pena said. "You buy these supplies, and you are the disaster."