Pulse oximeter apps: can your phone really check your oxygen level?

Short answer

No ordinary phone app can reliably measure your blood oxygen with the camera alone. In an emergency-department study of 191 adults, two camera-only iPhone oximeter apps barely tracked a hospital pulse oximeter (correlation 0.015 and 0.112) and missed most people whose oxygen was low; the authors said such apps "should not be recommended" where oxygen status matters (3). A research prototype did better, but its own authors called it "insufficient for medical use" (4).

If you need a number you can act on, use a fingertip pulse oximeter. A normal reading is 95% to 100%. Call your doctor if a home reading is 92% or lower, and get medical help right away at 88% or lower (1). Even a real oximeter has limits: dark skin, cold fingers, nail polish and poor circulation can all skew it (2).

If you've been wondering whether checking your oxygen at home is overkill: it's not hypochondria, and you're not imagining the breathlessness. Wanting a number when you feel short of breath is reasonable; the point is to get one you can trust.

Note: this article is for general education and is not medical advice. Shortness of breath, bluish lips or nails, confusion or chest pain are reasons to seek care right away, whatever any device says. Do not rely on an app or a watch to decide whether you need medical help. This guide is published by Welltory, which makes one of the apps mentioned. Welltory is a general wellness product: it does not measure blood oxygen and does not diagnose or treat any condition.

What a pulse oximeter actually measures

A pulse oximeter estimates SpO2, the percentage of hemoglobin in your blood that is carrying oxygen. It does this with light. A standard fingertip clip shines red and infrared light from small LEDs through your finger and measures how much comes out the other side (4). Oxygen-rich and oxygen-poor blood absorb those two colors differently, and the device turns the ratio into a percentage. It also counts your pulse from the same signal.

The "real" test is an arterial blood gas: a blood sample from an artery, analyzed in a lab. Your pulse oximeter result "may be slightly higher or lower" than that, and the blood test is more accurate (1). A fingertip device is a good estimate, not a perfect one.

Our guide to normal blood oxygen levels covers what each number means in more depth, and how blood oxygen is measured explains the clinical methods.

Can a phone camera measure blood oxygen?

Not well enough to trust, for one main reason: your phone doesn't have the right light.

A phone camera app works by reflection. You cover the lens and flash with a fingertip, the white flash lights up the skin, and the camera records tiny color changes as blood pulses through. That signal is good for counting heartbeats. It is much weaker for oxygen, because the phone has no infrared emitter. Researchers who built a phone oximeter had to work around this by using the camera's blue, green and red channels instead of red and infrared, and noted it was not possible to capture all three at the ideal exposure at once (4).

So when a free app on the App Store or Google Play shows "SpO2 98%" after you cover the camera, it's worth asking where that number came from. Most of these apps don't publish validation data, and the ones that have been tested independently did poorly.

What the studies found

Camera-only apps in a real emergency department

The most direct test is a 2019 study from the University of Alabama at Birmingham. Researchers took readings from 191 adults in an emergency department with a hospital pulse oximeter and with three iPhone apps, in random order (3):

• Two apps used only the phone camera and flash.

• One app used an external red-light probe plugged into the phone.

The hospital device found that 35.6% of patients had oxygen at or below 94%. One camera-only app flagged just 9.4% of patients as low, and the other flagged none. Their readings had almost no relationship with the real numbers (correlation 0.015 and 0.112, where 1.0 would be perfect) (3).

The app with the external probe did better: it caught 69.1% of low readings. That still meant roughly a quarter of patients were misclassified (3). The authors concluded that patients and clinicians should be told these apps are not equivalent to standard pulse oximetry.

A research prototype under controlled conditions

In 2022, a University of Washington team tested a phone-camera method in six healthy volunteers while slowly lowering the oxygen they breathed, so their SpO2 moved between 70% and 100% (4).

• The average error was 5 percentage points. That's the difference between a reading of 95% (normal) and 90% (worrying).

• For spotting SpO2 below 90%, it was right about 8 times out of 10 (sensitivity 81%, specificity 79%).

• Only one of the six volunteers had dark skin, so the authors said they could not draw conclusions about skin tone.

• Their own verdict: "the current model is insufficient for medical use."

That's a promising research result, not a product you can download. It's also a useful benchmark: if a carefully built research method in a lab still misses by about 5 points, a random free app is unlikely to do better.

What this means in plain terms

Checked November 6, 2026.

Why skin tone matters for every oximeter

This isn't only an app problem. Pulse oximeters of every kind can read too high in people with darker skin, which is the dangerous direction: the screen says you're fine when you're not.

In a landmark 2020 analysis of nearly 48,000 paired readings in hospital patients, researchers looked at people whose oximeter said 92% to 96%, which looks reassuring. In one hospital, 11.7% of Black patients actually had arterial oxygen below 88%, compared with 3.6% of White patients. In a larger multicenter group the figures were 17.0% and 6.2%. That's nearly three times as often (5).

The FDA has listed skin pigmentation among the factors that affect accuracy since its 2021 safety communication (2). In January 2025 it issued draft guidance on how manufacturers should test medical pulse oximeters, including performance across skin tones (6).

What to do with this if you have darker skin:

• Treat a "borderline normal" reading with extra caution, especially 92% to 95%.

• Watch the trend, not one number. A drop from your usual reading means more than any single result.

• Let symptoms lead. If you feel breathless or unwell, don't let a normal-looking number talk you out of calling a doctor.

Other things that can throw off a reading

The FDA and Cleveland Clinic list several factors that can make any pulse oximeter less accurate (1, 2):

• Cold hands and poor circulation

• Dark nail polish or long or thick artificial nails

• Thick skin or calluses

• Tobacco use and carbon monoxide exposure

• Some blood disorders

• Unclean skin

Movement is the other big one. Phone apps are especially sensitive to it, because the fingertip has to stay perfectly still on a lens. Even Welltory's own camera guidance warns that any finger movement can distort the reading (10).

How to check your oxygen level at home, step by step

If you want a reading you can actually use, here's how to take one with a fingertip pulse oximeter:

1. Sit down and rest for five minutes. Activity changes both pulse and oxygen for a while.

2. Warm your hands if they're cold. Rub them together or hold a warm mug.

3. Remove nail polish or artificial nails from the finger you'll use, or choose a bare finger.

4. Clip the oximeter onto your index or middle finger, nail side up, with your hand resting at heart level.

5. Stay still and quiet. Don't talk or move your hand.

6. Wait for the number to settle. It often moves for the first several seconds. Use the reading once it's been steady.

7. Check the pulse number too. If the pulse shown doesn't roughly match a pulse you count yourself at the wrist, the oxygen reading may be unreliable. Our guide to checking your pulse shows how.

8. Write it down with the time, the finger used and how you felt.

If your doctor gave you a target range, use theirs. People with long-term lung disease, and people who live at high altitude, may normally run lower than 95% (1).

What smartwatches can and can't do

Many watches now have a blood oxygen sensor at the wrist. They're more than a phone camera, because they have dedicated light sensors pressed against skin, but they're still sold as wellness tools.

• Samsung Galaxy Watch. You can take a spot reading in Samsung Health: open Blood Oxygen, rest your hand on a table close to your heart and keep still. Samsung advises resting at least five minutes first and wearing the watch snug on top of the wrist. It states that "Galaxy Watch is not a medical/therapeutic device and is not intended for medical use" (8).

• Apple Watch. In August 2025 Apple announced a redesigned Blood Oxygen feature for some US models (Series 9, Series 10 and Ultra 2), where the watch collects the data and the paired iPhone calculates the result, which then appears in the Health app (7).

Where a watch helps most is overnight and over time: seeing whether your readings dip during sleep, or whether your usual range shifts during a cold or at altitude. For a single spot check, a fingertip oximeter is the better tool, and symptoms still come first. We go further into the overnight side in our guide to low blood oxygen.

When a phone app is still useful

Phone apps aren't useless. They're just good at a different job.

• Heart rate. Camera apps read your pulse from the same fingertip signal. Heart rate is a simpler signal than oxygen, and the validation picture for it is different. Our article on how accurate HRV from a phone camera is goes through the validation evidence.

• Logging readings from a real device. Many fingertip oximeters pair with an app by Bluetooth, which saves you writing numbers down. "Pulse oximeter with app" usually means this: the oximeter measures, the app stores.

• Seeing the bigger picture. An app that puts your oxygen readings next to sleep, heart rate and how you felt can show patterns a single reading can't.

What a phone app can't do is replace the light source and sensor a real oximeter has.

How to choose a home pulse oximeter

You don't need anything fancy. A few things make a difference:

• Know what you're buying. Prescription oximeters are reviewed by the FDA and clinically tested. Many over-the-counter fingertip models are sold as general wellness or sports and aviation products and don't go through FDA review (2). If accuracy matters for a health condition, ask your doctor or pharmacist which model they recommend.

• A clear display that also shows pulse rate and, ideally, a signal-strength bar, so you know when the reading is steady.

• A snug fit on your finger, neither loose nor painfully tight.

• Bluetooth logging if you need to send readings to a doctor.

Common mistakes with oxygen apps and oximeters

• Trusting a camera app's SpO2 number. If it shows 98% while you feel breathless, the number is the thing to doubt.

• Taking a reading right after walking upstairs. Rest first.

• Measuring with cold fingers or through nail polish.

• Reading the first number that flashes up rather than waiting for it to settle.

• Ignoring the pulse number. If the pulse is wrong, the oxygen reading probably is too.

• Comparing one reading against a chart instead of against your own usual range.

• Letting a normal reading override symptoms. The FDA's advice is plain: don't rely only on a pulse oximeter, and pay attention to how you feel (6).

Living with oxygen worries: the questions people ask next

Is there a free oxygen level app for Android?

There are many free apps that claim to read SpO2 with the camera, but independent validation for them is hard to find, and the camera-only apps that were tested performed poorly (3). If you have a Galaxy Watch, Samsung Health can take a wellness spot reading (8). For a reliable number, use a fingertip oximeter.

Can I check my oxygen level on my iPhone without a watch?

Not reliably. The iPhone camera can read your pulse, but it has no infrared light for oxygen. Apple's own blood oxygen feature needs a compatible Apple Watch (7).

Why does my oxygen app say 99% when I feel short of breath?

Because the app may be producing a number that has little to do with your blood. Camera-only apps tend to show reassuring numbers even when oxygen is low: one app in the emergency-department study flagged no one as low at all (3). Trust the symptom, not the app.

What oxygen level is too low?

For most adults, 95% to 100% is normal. Contact a provider at 92% or lower, and get medical help right away at 88% or lower (1). Your doctor may give you a different target if you have lung disease.

Do I need a pulse oximeter at home?

Most healthy people don't. It can be helpful if you have a lung or heart condition, if your doctor asked you to monitor during an illness, or if you're recovering from a respiratory infection. Ask your doctor whether it makes sense for you and what number should prompt a call.

Before you blame yourself

Maybe you've been feeling winded on the stairs and told yourself you're just out of shape, or that you're being dramatic for wanting to check. Before you blame yourself, check what your body already recorded.

Breathlessness often has a cause you can see: a cold that's lingering, a few nights of poor sleep, a resting heart rate that's crept up, or a stretch of less activity than usual. Those leave traces in your heart rate, sleep and energy before you'd ever think to measure oxygen.

Pick one thing to watch for one to two weeks. For example, take a fingertip oximeter reading each morning at rest and note how you slept and how you feel. If the readings stay in your usual range and you feel better as the cold clears, that's reassuring. If they drift down, or the breathlessness doesn't ease, you have a clear record to take to your doctor.

When to see a doctor

Contact a doctor if:

• your home pulse oximeter reads 92% or lower (1);

• you notice increasing or worsening symptoms, or you're worried about your readings (2);

• you're short of breath with normal activity, or it's getting worse over days;

• you have a lung or heart condition and your readings are lower than your usual range.

Get medical help right away if your reading is 88% or lower (1), or if you have signs of low oxygen such as severe shortness of breath or bluish coloring of the face, lips or nails (2). Call 911 or your local emergency number if you can't catch your breath, have chest pain or are confused.

How to bring this up with your doctor

What to ask for, by name. "Could you check my oxygen saturation in the office and tell me what range is normal for me?" If symptoms happen at night: "Would an overnight oximetry test or a sleep study make sense?" If you have darker skin: "Should we confirm with an arterial blood gas if my oximeter readings look borderline?"

What to bring. Your home oximeter (so they can compare it with theirs), a log of readings with dates, times and how you felt, and a list of medicines.

What to say, out loud. "My readings at rest are usually around [number], but when I [walk upstairs/wake up], I feel [breathless/dizzy] and it drops to [number]."

If you're told it's anxiety. Ask: "Could we rule out a lung or heart cause first, for example with an oxygen check after walking?"

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How Welltory helps — and what it cannot do

The limits first. Welltory is a general wellness product, not a medical device. It does not measure blood oxygen, with the camera or any other way (9). It does not diagnose low oxygen or any lung or heart condition, and it isn't a substitute for a pulse oximeter or a doctor.

What it can do is help you see your readings in context:

Keep your SpO2 next to the rest of your data. If a watch or oximeter records oxygen saturation and shares it with Apple Health, Health Connect or Samsung Health, Welltory can store it and chart it in My data → Health, and look for links with HRV, workouts and other activities (9). Which devices pass oxygen data through depends on the source, so check the list of supported devices first (11).

Heart rate and HRV with your phone camera. You can take a spot reading of heart rate and HRV by covering your phone's camera and flash with a fingertip (10). This is a short, deliberate measurement, not continuous monitoring, and it's not for oxygen. Some phones, including Google Pixel models, can't take camera readings because the flash is too far from the lens (10).

Tag what's going on in My Patterns. On iOS, when Welltory notices a stress or recovery episode, you can tag what happened, such as "cold", "bad night" or "short of breath", so patterns are easier to spot later (12).

A record for your doctor. From the web app you can export your data as CSV: Dashboard → choose a chart → pick the time range → Export (13).

If you want to raise your numbers rather than just track them, our guide to improving blood oxygen levels covers what helps.

How we made it

We based this article on Cleveland Clinic's guide to pulse oximetry, the FDA's 2021 safety communication and its pulse oximeter page, an emergency-department study of iPhone oximeter apps, a controlled study of smartphone camera oximetry, and an analysis of racial bias in pulse oximetry published in the New England Journal of Medicine. Device details come from Apple's and Samsung's own pages, checked on November 6, 2026. Search questions came from what people in the United States most often ask about pulse oximeter apps and checking oxygen with a phone. For the product section, we checked every function against the Welltory Help Center on November 6, 2026.

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Jane Smorodnikova, co-founder of Welltory, built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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