Pulse oximeters are an unlikely home health essential. The device checks vital statistics like blood oxygen levels, heart rate, and blood pressure, and while these numbers may not mean much to the general public, they help medical professionals gain a better understanding of your overall health, especially during this pandemic. In fact, doctors started recommending patients purchase pulse oximeters to track coronavirus symptoms earlier this spring. 

A popular op-ed for The New York Times written by emergency physician Richard Levitan, MD revealed that critically ill COVID-19 patients often arrived at the hospital with dangerously low oxygen levels—an issue that using a pulse oximeter could help prevent. Because the at-home device screens for low oxygen levels, which is an early warning sign of illnesses like pneumonia, it gives patients better insight on when to seek professional help. 

The connection made pulse oximeters just as hard to buy as toilet paper, disinfectants, and thermometers—but now, the at-home version of the medical tool is back in stock. Sellers on Amazon have ample supply, and prices have gone back to their pre-COVID norms of around $30 for a basic pulse oximeter. (Note: Many of these devices are not FDA-approved and recommended for sport or aviation use only. While shoppers report accurate statistics similar to readers at their doctor’s office, these at-home finds should not be expected to offer the same level of accuracy.)

A pulse oximeter works by transmitting a wavelength of light through your finger, earlobe, or toe. According to the World Health Organization, this light finds hemoglobin—the protein in your blood that carries oxygen—and the amount absorbed by the protein varies based on how much oxygen is already saturating it. A sensor on the other side of your extremity then calculates your blood oxygen levels based on the light wavelengths received, along with your blood pressure and pulse rate.

To get the best at-home reading, it’s important to complete the reading on a finger without any nail polish that’s ideally warm, according to a previous Health interview with Sharon Chekijian, MD MPH, an emergency medicine doctor with Yale Medicine. She also suggested trying to use the middle finger and paying close attention to the reading to ensure the device is continuously tracking your vitals—sudden dips and jumps could indicate you’re not using the pulse oximeter correctly.

Already an essential for those with asthma or other lung diseases, a pulse oximeter is an affordable investment that could give you peace of mind during the pandemic. It’s not only easy to use, but it gives valuable insight into your health that could be helpful to medical professionals. Below, we’ve highlighted the top-rated pulse oximeters on the market that are available to shop right now.