As someone who has personally struggled with sleep apnea, I know the anxiety of waking up exhausted, nursing a headache, and wondering why. I also know the frustration of buying a overnight pulse oximeter out of desperation, only to find out the data is junk.
To find the truth, I spent the last two months sleeping with over 20+ continuous pulse oximeters. Each device was compared against our $1500 Nonin 3150 Gold Standard blood oxygen monitor for three nights each.
Out of the 5 Wellue devices we tested, only one came out on top. Here is the full break-down of the most popular Wellue continuous pulse oximeters.
The rings are super comfortable, but only one device in this lineup earned our “Top Pick”.
Top Pick: Checkme O2 Max
The Checkme O2 Max provided oxygen monitoring accuracy, achieving a flawless +0.2% agreement bias and a 90.7/100 Overall O2 Score against our $1,500 hospital reference monitor. As an FDA-Cleared Class II medical device with a 72-hour battery, it is the ultimate tool for accurately troubleshooting CPAP therapy, tracking concerning overnight oxygen dips, or optimizing your sleep.
Pros:
Cons:
Test Protocol (Simple Version)
- The hospital-grade Nonin was wore on one hand, and a Wellue overnight monitor on the other
- Every morning, I exported the raw data files from both blood oxygen monitors
- Our custom built Python script cleaned, aligned, and compared the data line-by-line
- All the metrics were averaged across 3 nights to reduce randomness
Why the Checkme O2 Max Won (The Deep Dive)
This is the how all five Wellue devices tested performed for our Overall O2 Score; showing how close they agreed with our hospital-grade pulse oximeter line-by-line.
Hardware, Buttons & Build Quality
When you pull the Checkme O2 Max out of the box, it immediately feels like a premium piece of hardware. It has a high-gloss black finish, sleek design lines, and a smooth, robust band. It is the “Tesla” of the pulse oximeter world.
The design logic is incredibly streamlined. The device is equipped with a crisp display on the face, a tactile power button on the side, and a dual-purpose port for charging and connecting to a computer if you don’t want to use the bluetooth.
I personally enjoyed having a power button. Having the ability to start the monitoring when I got into settled into bed was nice. Some turn on automatically when sensing your skin touching.
However, the physical hardware does have two distinct annoyances you should know about:
The Clasp: The wrist clasp holds exceptionally well, meaning it will never fell off at night. But out of the box, it is mildly annoying to put on. You have to push quite hard to get it snapped onto your wrist, though it does get easier after several days of use. Might just be built for longevity.
The Left-Hand orientation: This monitor is explicitly designed to be worn on your left hand. If you wore it on your right hand, the screen would not auto rotate.
The Pillow Test: Sleeping With It
Another big win for the Checkme O2 Max is the finger sensor design. Many oximeters I tested had a restrictive sensor that pinches your finger, leaving it throbbing by 3:00 AM. Because the “brain” of this device sits on your wrist, the photosensor itself is incredibly lightweight on your finger, it is less noticeable while sleeping.
The location of the sensor on your hand and how much pressure it exerts to stay on all night is crucial. After testing overnight oxygen monitors for a combined 480 hours, trust me—being able to bend your finger is a massive deal. This sensor sits in a less sensitive area—at the base of your finger and allows it to naturally bend while you sleep.
It uses red and infrared LEDs to measure your blood oxygen saturation, housed in a soft silicone ring.
The Smart Alarm (Positional Therapy)
If you have a health condition like obstructive sleep apnea, COPD, or if you are a biohacker trying to train yourself out of mouth-breathing, the “Smart Alarm” is a necessary feature. The sensor has a strong vibration motor built right into the finger ring.
If your oxygen saturation levels or heart rate drops below a certain threshold that you set in the app, it vibrates. You can easily adjust this vibration from very weak to very strong. This isn’t just an alarm; it’s like a biofeedback loop. It acts as positional therapy, gently nudging you to roll off your back and open your airway before your blood oxygen level plummets further, often without fully waking you up.
The App & Data Export (The Ultimate CPAP Troubleshooting Tool)
If you are currently using a CPAP machine and wondering, “Is this thing actually working?”—or if you are a biohacker who lives in spreadsheets—this is your device. The free ViHealth app is incredibly intuitive and syncs thousands of rows of overnight data in seconds. It is a genuinely well-built app. I am sure syncing 13 different devices to it and downloading dozens of raw data files gave it a run for its money, and is far beyond its intended use, but it performed flawlessly!
You get a crystal-clear data display of your pulse rate and any early warning signs of oxygen dropping. By simply clicking the share icon, you can export a clean CSV , PDF, or Binary file.
The CSV file that the Vihealth app exports is clean and easy to work with.
I did test ISO and Android versions of the app and they functioned identically.
Pro-Tip for Sleep Optimizers: You can take the Binary file from the Checkme O2 Max and overlay it with your CPAP data in software like OSCAR to see exactly what is moving the needle on your continuous monitoring charts. This format gives your healthcare provider granular data that works flawlessly in sleep analysis algorithms and rivals an at-home sleep study.
O2 Insight Pro Access
The Checkme O2 Max is one of a handful of devices that has access to the computer software version. It offers more detail on the second-by-second sleep graphs that the Vihealth app doesn’t give you.
Checkme O2 Max Testing Data
Before we give our final verdict, here is the Checkme 02 data from our lab test. The Checkme O2 Max achieved an incredible 99.6% Signal Stability and a mathematically perfect +0.2% Bias against our hospital-grade pulse oximeter.
Chart Definitions
- ODI (3% & 4%): The “Oxygen Desaturation Index” counts how many times your oxygen drops per hour. 3% is a mild dip; 4% is severe. The 3% is a more sensitive metric.
- Time <90%: A timer counting every second you spent below 90% oxygen.
- Time <88%: A timer counting every second you spent below 88% oxygen.
- Lowest SPO2 (Nadir): The absolute lowest oxygen point of the night. We checked if the device caught this “rock bottom” moment or smoothed it over.
- Bias: Shows the device’s “personality.” Positive (+) bias means it overestimates oxygen (optimist); Negative (-) means it underestimates it (pessimist).
- Signal Stability: Measures how often the device stays within ±2% of the medical reference. High stability means it rarely loses its “lock” on your data.
- Overall O2 Score: A 0–100 final grade. It heavily weights ODI and Stability to determine if the device is safe for medical tracking.
The Overall O2 Score is calculated by the following weights: 40%: ODI Accuracy (3% and 4% combined) 30%: Signal Stability (FDA-style ±2% agreement) 20%: Nadir Accuracy 10%: T90 Accuracy.
The Verdict
I used to wake up every morning with a headache and zero energy, and I sincerely wish I had known about the Checkme O2 Max back then. After rigorously testing these oxygen monitors, this is the Wellue device I trust to catch the rapid oxygen drops that smartwatches completely miss. If you are tired of guessing why your sleep is broken, this gives you the exact second-by-second monitoring so you can finally get better sleep.
Wellue Checkme O2 Max
Pros:
Cons:
The Rest of the Wellue Lineup
The Checkme O2 Max took the top spot, but I tested them all. Let’s dive into the full showdown.
Here are the Score Cards for the rest of the Wellue pulse oximeters, showing how close they tracked our hospital-grade blood oxygen monitor.
Wellue Checkme 02 Ultra Score Card – Scroll through to see them all. 
Wellue SleepU Score Card – Scroll through to see them all. 
Wellue 02 Ring Score Card – Scroll through to see them all. 
Wellue O2 Ring S Score Card – Scroll through to see them all.
Chart Definitions
- ODI (3% & 4%): The “Oxygen Desaturation Index” counts how many times your oxygen drops per hour. 3% is a mild dip; 4% is severe. The 3% is a more sensitive metric.
- Time <90%: A timer counting every second you spent below 90% oxygen.
- Time <88%: A timer counting every second you spent below 88% oxygen.
- Lowest SPO2 (Nadir): The absolute lowest oxygen point of the night. We checked if the device caught this “rock bottom” moment or smoothed it over.
- Bias: Shows the device’s “personality.” Positive (+) bias means it overestimates oxygen (optimist); Negative (-) means it underestimates it (pessimist).
- Signal Stability: Measures how often the device stays within ±2% of the medical reference. High stability means it rarely loses its “lock” on your data.
- Overall O2 Score: A 0–100 final grade. It heavily weights ODI and Stability to determine if the device is safe for medical tracking.
The Overall O2 Score is calculated by the following weights: 40%: ODI Accuracy (3% and 4% combined) 30%: Signal Stability (FDA-style ±2% agreement) 20%: Nadir Accuracy 10%: T90 Accuracy.
Well O2Ring S (Overall O2 Score 81.1)
Comfort: 10/10 — invisible
Like the original O2Ring , from our tests, it suffers from a slight optimistic bias (+1.0%), meaning it reads your oxygen slightly higher than reality. Who is it for? If you absolutely refuse to wear a wrist strap with finger sensor to bed, but you still want 1-second interval data and modern USB-C charging, the Wellue O2Ring S the best standalone ring on the market.
Wellue O2Ring (Overall O2 Score 81.7)
Comfort: 10/10 — invisible
The original ring model actually had a “Perfect” mean bias (+0.7%). However, a perfect average doesn’t mean perfect tracking. It did not catch rapid desaturations like we hoped, missing over 51% of 3% drops.
It averages out nicely over the night, but smoothed over quick oxygen dip events, probably due to the 4s sample interval. But if you are just looking for a general sleep oxygen monitor on a budget, and comfort needs to be the highest then the Wellue O2Ring would be the one to grab.
Wellue SleepU (Overall O2 Score 87.8)
Comfort: 9/10
Like the Checkme O2 Max, this uses the exact same finger sensor, but our tests show it reads slightly optimistic and emits an annoying (but brief) bright blue light when first turned on.
Who is it for? If you want a secure wrist-and-finger fit but need a device that is budget-friendly, nearly half the weight (31g vs 56g), and simplified with zero buttons, a good alternative is the Wellue SleepU.
Wellue Checkme O2 Ultra (Overall O2 Score 87.3)
Comfort: 7/10
The Ultra features premium build quality and a incredibly satisfying magnetic charger, but our lab data shows it slightly smooths over rapid oxygen dips. It is also strictly locked to a left-hand display.
Who is it for? If you need hyper-fast apnea detection, skip this. But if you travel frequently, despise daily charging, and just want a general oxygen baseline backed by a massive 100+ hour battery life and four days of on-device memory, a good premium alternative would be the Checkme O2 Ultra.
Bonus Data
Since we’ve already covered the final scores and how we tested them at a high-level, this next section is strictly for the data nerds who want to look a little more under the hood.
To get those exact scorecard calculations, we didn’t just read the back of the box. We spent hundreds of hours designing a rigorous testing protocol, meticulously controlling our variables, sleeping with them night-after-night and running line-by-line data comparisons against our $1,500 hospital pulse oximeter.
If you want to see exactly what that raw data looks like, below is the actual 3-Night Deviation Chart for the Checkme O2 Max.
Chart with 25,000 rows of data. Clearly shows why it scored 99.6% on Signal Stability 😀 
Chart with 25,000 rows of data. Clearly shows why it scored 99.6% on Signal Stability 😀 
Chart with 25,000 rows of data. Clearly shows why it scored 99.6% on Signal Stability 😀
How to Read this Chart
Think of the Blue Line as the device’s “Report Card.”
- The Center Line (0): This is a perfect score. The device matched the medical equipment exactly.
- The Pink Lines (+2 /-2): These are the “Guard Rails”. As long as the blue line stays between them, the Checkme O2 Max is considered perfect alignment with the hospital-grade device.
- The Takeaway: Notice how the blue line spends almost the entire night safely inside the tracks. This is what reliability looks like.
Deviation Calculation
- The “Zero-Blindspot” Formula: We calculate the deviation for every single second of sleep using this formula:
- Deviation = SpO₂ (Reference) – SpO₂ (Test Device)
- The “Safety Guard Rails” (ISO 80601-2-61): You will see the pink limit lines at ±2%. These aren’t arbitrary; they represent the International Standard (ARMS) for clinical pulse oximetry.
- Why this matters: If the device’s line stays between these rails, it is agreeing with the hospital equipment.
- Bias Direction (The “Life Saving” Metric):
- Optimistic Bias (Negative Score): The line dips DOWN. Those are more dangerous because the device is reporting higher oxygen levels than you actually have, potentially masking a problem.
- Pessimistic Bias (Positive Score): The line trends UP. This is safer because the device is slightly under-reading, ensuring you are alerted to drops early.
- The “Fair Start” Protocol: To be 100% fair to the hardware, we surgically trim the first 5 minutes of every recording. This removes “warm-up” noise and ensures we only grade the device once it has stabilized on our finger.
Wellue Checkme O2 Max
Pros:
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