Pulse Ox is a blood oxygen monitoring feature built into many Garmin smartwatches. It uses sensors on the back of the watch to estimate how much oxygen your red blood cells are carrying, expressed as a percentage called SpO2. A healthy reading typically falls between 95% and 100%, and Garmin flags readings below 92% as potentially low.
How the Sensor Works
The back of a Pulse Ox-equipped Garmin watch has small LEDs that shine red and infrared light into your skin. Oxygenated blood and deoxygenated blood absorb these wavelengths differently. By measuring how much light passes through versus how much gets absorbed, the watch calculates the ratio of oxygenated to total hemoglobin in your bloodstream. This is the same basic principle hospitals use with fingertip pulse oximeters, just adapted for your wrist.
To take a reading, the watch needs to be snug against your skin with minimal movement. You can trigger a spot check manually by opening the Pulse Ox widget and holding still for about 30 seconds, or you can set the watch to monitor continuously throughout the day or only during sleep.
What the Readings Mean
Medical experts at the Mayo Clinic consider 95% to 100% a normal blood oxygen range for most people. Below 92% is generally considered low and can be associated with health issues that need medical attention. Your Garmin will display your SpO2 as a single percentage, and if you use all-day or sleep tracking, you’ll see trends over time in the Garmin Connect app.
Several things can shift your readings without anything being wrong. Higher altitude naturally lowers SpO2 because the air is thinner. Physical activity, your body position, and even how tightly the watch sits on your wrist all play a role. Garmin recommends wearing the watch above the wrist bone (closer to your elbow) rather than right on the bony part, and research backs this up. One study testing a Garmin Fenix 6 Pro found that readings taken below the wrist bone were significantly less accurate than those taken higher on the forearm.
How Accurate Is It?
Garmin is upfront that Pulse Ox is not a medical device. Independent testing confirms there are real limitations. In a study published in the Journal of Health Technology Assessment and Management, researchers compared SpO2 readings from a Garmin Fenix 6 Pro against a medical-grade fingertip oximeter. Out of 100 test measurements, 53 failed to meet clinical standards. Of those failures, 38 were inaccurate readings (off by more than 3 percentage points), and 15 were cases where the watch couldn’t produce a reading at all after two attempts. The Garmin consistently read lower than the medical device across all test conditions.
That doesn’t make the feature useless. It means you should treat it as a trend tracker rather than a diagnostic tool. If your readings are consistently in the mid-90s and then drop to the low 80s for several nights in a row, that pattern is worth paying attention to, even if any single number isn’t perfectly precise. But a one-off reading of 91% while you’re moving around or wearing the watch loosely isn’t necessarily cause for concern.
Tracking Modes and Battery Impact
Most Garmin watches with Pulse Ox offer three modes: off, sleep only, and all-day. The mode you choose has a major effect on battery life. Enabling all-day Pulse Ox can cut your battery life roughly in half compared to keeping the feature turned off. Even sleep-only tracking adds noticeable drain. On a Forerunner 245, for example, users report losing about 5% battery overnight with sleep Pulse Ox enabled, which adds up over a week.
Sleep-only mode is the most popular compromise. It gives you nightly SpO2 data (useful for spotting patterns related to breathing disruptions during sleep) without draining the battery during the day when movement makes readings less reliable anyway. If you only want an occasional check, spot readings use negligible battery and give you a quick snapshot whenever you want one.
Altitude Acclimation
One of the more practical uses for Pulse Ox on a Garmin watch is tracking how your body adjusts to high altitude. Several Garmin models include an altitude acclimation widget that combines your weekly average SpO2 with respiration rate and resting heart rate to give you a picture of how well you’re adapting. If you’re hiking at elevation or traveling to a high-altitude destination, watching your SpO2 trend upward over several days is a reassuring sign that your body is adjusting. This feature requires all-day Pulse Ox to be enabled, so expect the extra battery drain during trips where you’re using it.
Tips for Better Readings
- Stay still. Movement is the biggest source of errors. For spot checks, sit down and rest your arm on a flat surface.
- Wear the watch snugly above the wrist bone. Research shows readings taken closer to the hand are less accurate than those taken a finger’s width above the bony bump on your wrist.
- Wait a few minutes after exercising. Blood flow changes during activity can throw off the sensor.
- Check skin contact. Tattoos, thick wrist hair, or a loose band can block the light from reaching your blood vessels properly. If the watch displays a “Check Fit” error, tighten the band and try again.
- Look at trends, not single readings. One low number can be a sensor glitch. A consistent pattern over multiple nights tells you something real.
Pulse Ox is available on most of Garmin’s mid-range and premium watches, including models in the Fenix, Forerunner, Venu, Enduro, and Instinct lines. Budget models like the basic Forerunner 55 or entry-level Vivoactive watches may not include the hardware. Garmin also notes that Pulse Ox is not available in all countries due to regulatory differences.