Pulse Oximeters: What to Know Before You Buy

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You may have seen a pulse oximeter clipped to a patient's finger in a doctor's office or hospital. Much like how a thermometer reads your temperature, a pulse oximeter detects how much oxygen is in your blood. It also reads your heart rate. Unlike a thermometer, which you likely have in your home, these oxygen level testers have typically been less common in a home medicine cabinet.

However, since the COVID-19 pandemic, the pulse oximeter has made its way into many more medicine cabinets. This device can provide an accurate picture of how our lungs are faring. Sometimes, it's hard to distinguish milder symptoms from those that warrant emergency medical care, which is where a pulse oximeter can help.

Learn more about pulse oximeters, including what you need to know if you want to buy one.

Having an at-home pulse oximeter may be recommended if you are at high risk of complications from COVID or other respiratory illnesses.

"Many doctors have been advising patients, especially those with worrisome symptoms or chronic health conditions like heart or lung problems, to buy a pulse oximeter for home to monitor their oxygen levels without trekking to the doctor or (emergency department)," Sharon Chekijian, MD, MPH. associate professor of emergency medicine at Yale Medicine, told Health.

While pulse oximeters are not a necessity for a person who is generally in good health, some healthcare providers suggest having one if you have preexisting breathing issues like asthma, COPD, or other lung diseases, and in case you contract COVID.

A pulse oximeter, also called a pulse ox, is a device that measures oxygen saturation levels, or O2 sat, in your blood. A pulse ox measures your peripheral O2 sat since it's detected externally on the finger, toe, or ear. Your blood—specifically proteins in your red blood cells called hemoglobin—carries oxygen and delivers it to your tissues, without which they couldn't function.

"The device transmits wavelengths of light to a sensor which calculates your blood oxygen saturation," George Fallieras, MD, medical director of BioCorRx and doctor at LA Surge Hospital, told Health. That wavelength targets the hemoglobin, and the light absorbed by the blood varies with the oxygen saturation of hemoglobin. It then transmits a numerical reading.

Pulse oximeters also measure pulse rate, or heartbeats per minute, showing how well the body's tissues are supplied with blood and the oxygen the blood transports.

A pulse oximeter can help detect or monitor breathing issues associated with COVID or COVID pneumonia. The device can be especially helpful if you are experiencing shortness of breath with diagnosed COVID—either to keep an eye on progress or to determine when it's worth an emergency room visit.

If you're using an at-home pulse oximeter, the device will clip onto your finger, toe, or earlobe. Start by sitting down and clipping the pulse ox onto your middle finger. Be sure to remove any nail polish, avoid using it on cold fingers, and sit still to get a correct reading. Also, disinfect it thoroughly before and after use, particularly if you use somebody else's device.

In addition to the reading and depending on the device, you might notice a tracing that looks like an S-shaped smooth, continuous wave. "The wave (called a sine wave) varies with your breathing. This means the device is really picking up the right signals. This is especially important if the reading looks low, so you don't misinterpret it," said Dr. Chekijian.

If the reading is low but you see a squiggly line instead of a regular sine wave, you are probably not getting a strong (or accurate) reading.

A reading between 95% and 100% is normal. Anything under 94% should be evaluated by a medical professional. A pulse oximeter reading of anything below 90% is considered a "clinical emergency" and should be treated urgently. A normal heart rate for an adult is between 60 and 100 beats per minute.

"If you do think you have COVID and you're using the pulse oximeter to measure your oxygen level, be sure to make a log of the readings so you can see if there are any changes," said Dr. Chekijian. Also, the numbers aren't the only thing you should focus on. She suggested noting how you were feeling at the time of the reading, whether you felt fine or were experiencing shortness of breath, for example.

Regardless of your reading, contact a healthcare provider if you have trouble breathing or other concerns or questions.

As with any at-home test, there is always a chance for faulty readings or incorrect use. The World Health Organization prompts medical professionals to rely on their clinical judgment versus a reading on the device. If you get a strange reading at home and you're not feeling ill, you can check the device's accuracy on another healthy family member. If you're uneasy about a reading and how you're feeling, it's best to seek medical attention.

It's also important not to let a good pulse oximeter reading give you a false sense of security if you're feeling unwell. If you're feeling lousy—shortness of breath, cough, fever, or other worrisome symptoms, check in with a healthcare provider.

The devices are sold online, at drug stores, or via medical equipment suppliers.

A word of caution: Do not rely on cellphone apps. While some apps for smartphones claim to measure oxygen levels, research shows they are not reliable enough to use in place of a pulse oximeter. Instead, stick to at-home finger pulse oximeter devices.

If you don't have a pulse oximeter and you're worried about your levels, check in with a healthcare provider to see if you can get a reading. "If you feel like you can't catch your breath or are winded with activity please visit a minute clinic, urgent care, or call your doctor to see if you can be seen," said Dr. Chekijian. "If it's after hours, call 911 or proceed to the emergency department."

If you are at higher risk of complications from COVID, flu, or other respiratory illnesses, you may consider buying a pulse oximeter to monitor your blood oxygen levels at home. These devices are relatively easy to use and can be helpful to gauge how your lungs are functioning. Call a healthcare provider if you have any questions about your breathing and whether or not (and how) to use a pulse oximeter.

Centers for Disease Control and Prevention. Symptoms of COVID-19.

National Heart, Lung, and Blood Institute. Updating Pulse Oximeters.

World Health Organization. Pulse Oximetry Training Manual.

Hafen BB, Sharma S. Oxygen Saturation. [Updated 2022 Nov 23]. In: StatPearls. Treasure Island (FL): StatPearls Publishing.

World Health Organization. Interim Guidance for Member States - On the Use of Pulse Oximetry in Monitoring Covid-19 Patients Under Home-Based Isolation and Care.

Luks AM, Swenson ER. Pulse Oximetry for Monitoring Patients with COVID-19 at Home. Potential Pitfalls and Practical Guidance. Ann Am Thorac Soc. 2020;17(9):1040-1046. doi:10.1513/AnnalsATS.202005-418FR