SpO2 (blood oxygen saturation) measures the percentage of haemoglobin in your blood that's carrying oxygen. A reading of 95-100% is normal for healthy adults. Fitness trackers measure SpO2 using red and infrared LED sensors on the back of the device, which detect how oxygen-rich blood absorbs light differently from oxygen-depleted blood. The Qorfit Pulse monitors SpO2 continuously and alerts you if readings fall below a threshold you set.
The first time most Indians heard the term SpO2 was probably sometime in 2020 or 2021, when pulse oximeters became as hard to find as hand sanitiser. Suddenly, everyone was clipping little plastic devices onto their fingers and reading out numbers at the dinner table.
The pandemic changed something; it made people realise that blood oxygen is something you can actually monitor at home. And now, that same monitoring capability sits right on your wrist, inside a fitness tracker.
But what does SpO2 actually mean? When should you be concerned? And how does a device on your wrist measure something that sounds like it should require a hospital?
What SpO2 Actually Means
SpO2 stands for 'saturation of peripheral oxygen'; it's a measure of how much of your haemoglobin (the protein in red blood cells that carries oxygen) is actually loaded with oxygen as it circulates through the capillaries near your skin.
Think of your red blood cells as tiny delivery trucks. SpO2 tells you what percentage of those trucks are carrying cargo (oxygen) right now. At 98%, 98 out of every 100 trucks are full. At 90%, only 90 are, and that starts creating problems for your organs, which depend on a steady oxygen supply.
For context: healthy lungs in a healthy person at sea level typically maintain SpO2 between 95 and 100%. Anything consistently below 94% warrants attention. Below 90%, especially if you feel breathless or dizzy, is a medical red flag.
How Your Fitness Tracker Measures SpO2
Here's where the technology gets genuinely clever. Fitness trackers use a method called photoplethysmography, the same PPG technology used for heart rate monitoring, but with two different wavelengths of light: red (around 660nm) and infrared (around 940nm).
The reason for two colours isn't arbitrary. Oxygenated haemoglobin absorbs infrared light more readily and lets more red light pass through. Deoxygenated haemoglobin does the opposite. By shining both wavelengths into your wrist and measuring how much of each bounces back, the sensor can calculate the ratio of oxygenated to deoxygenated blood.
That ratio becomes your SpO2 reading.
Learn: How does it work?
One important caveat: wrist-based SpO2 readings are estimates, not clinical measurements. They're accurate enough to catch trends and obvious problems, but a dedicated fingertip pulse oximeter (or a hospital-grade reading) will always be more precise. This doesn't make wrist-based monitoring useless; quite the opposite. Continuous monitoring catches gradual declines that a single spot-check would miss entirely.
NOTE FOR INDIA: If you live at a high altitude in Shimla, Mussoorie, Ladakh, Darjeeling, or the hills of the Northeast, expect naturally lower SpO2 readings. At 2,000 metres above sea level, a resting SpO2 of 92-94% can be completely normal. Your baseline in the hills is different from your baseline in Chennai or Pune.
What Is a Normal SpO2 Reading?
For healthy adults at sea level, 95-100% is the standard healthy range. Let's break it down:
- 96-100%: Normal. Your body is well-oxygenated. No action needed.
- 94-95%: Borderline. Worth monitoring more closely, especially if you feel any shortness of breath.
- 90-93%: Low. Consistently reading in this range needs a doctor's review.
- Below 90%: Hypoxaemia. This is a medical concern and warrants prompt attention.
Important: a single low reading doesn't mean much. Fitbits and smartbands are sensitive to movement, cold hands, dark skin pigmentation (which can slightly reduce sensor accuracy), and improper fit. If you get one concerning reading, adjust the band, warm your hands, and read again.
When SpO2 Monitoring Actually Matters
Continuous SpO2 monitoring shines in a few specific situations:
1. Sleep Apnoea Detection
This is probably the most underappreciated use case. Sleep apnoea, where your breathing repeatedly stops during sleep, is common in India, heavily underdiagnosed, and genuinely dangerous if untreated. During an apnoea event, your SpO2 drops. A fitness tracker monitoring SpO2 overnight can flag these drops, giving you data to take to a doctor. It won't diagnose sleep apnoea, but it can give you a compelling reason to get a formal sleep study done.
2. High Altitude Travel
If you're heading to Leh-Ladakh for the summer, trekking in the Himalayas, or even visiting hill stations above 2,000 metres, your SpO2 monitoring becomes genuinely useful. Altitude sickness starts quietly, and tracking SpO2 gives you an objective early warning before symptoms become serious.
3. Respiratory Illness
During any respiratory illness, flu, severe cold, or chest infection, SpO2 monitoring can help you track whether things are getting better or worse. This became a critical use case during COVID-19, and it remains relevant today.
Track SpO2, heart rate, HRV, and BP 24/7 with Qorfit Pulse - India's smartest screenless health tracker under ₹9,000. qorfit.in
SpO2 vs Pulse Oximeter: Which Is More Accurate?
A fingertip pulse oximeter will always be more accurate than a wrist-based tracker. The fingertip has thinner skin, more capillaries, and a better light path, leading to fewer interference issues.
But here's the thing: accuracy at a single point in time is less valuable than you might think. The real value of wrist-based SpO2 is continuous monitoring, catching patterns across hours of sleep or activity that a single fingertip reading would never reveal. Use them for different purposes.
For peace of mind after a one-off reading on your tracker that concerns you, confirm with a fingertip oximeter or a doctor. Don't make health decisions based on a single wrist reading.
Read more: What Is HRV in a Fitness Tracker? | What Is a Health Tracker? | Health and Fitness Tracker
