I have sleep apnea. And I was like a lot of people here wasting money on cheap overnight sleep trackers, or expensive smart watches before realizing I had no idea if the data was actually accurate and I certainly was not getting consistent results across them.
So I spent two months doing something about it. I bought over 20 continuous overnight pulse oximeters and tested as many as I could get raw data out of, and here I will go over testing them, the science behind these devices, and how to properly use them.
Here's what the setup looked like every single night:
Nonin 3150 Testing
Every night I wore a Nonin 3150 on one hand (a FDA cleared hospital grade monitor used in actual clinical sleep studies) and the consumer device on the other. Both running simultaneously all night. Every morning I exported both raw data files and ran them through my custom coded Python script that aligned and compared the readings second by second. Each device got 3 nights of testing and all metrics were averaged across those nights to reduce randomness. I know I am a data nerd.
54 nights total. A few devices got cut early because they wouldn't hand over the raw data, and well... I'll get to the blister situation in a second. Apparently, pressure and them LED lights blasting your tip can start to hurt. Hell of a blister! I know your thinking, "wow, I hope the doctor could reattach that." Hey, when you have to wear a device for 8 hours, that little blister hurts bad, it disturbs your sleep A LOT.
But after a few nights of healing I continued.
Your Smart Watch and Garmin probably can't screen you for sleep disorders.
The thing that I have had so many conversations with people about, is that their Apple Watch or Gamin, or Fitbit says they breathe perfect at night. These devices are amazing for lots of things but reading your oxygen levels second to second all night is not one of them.
Smart Watches intermittently check your oxygen every "minutes", not seconds. It is impossible for those devices to know whether your oxygen is dipping for 10 seconds to 89%. They just provide high-level wellness average not a sleep disorder tool.
This is why I tested these dedicated continuous pulse oximeters, they have the ability to see in seconds, not minutes.
So, if you wake up with a headache in the morning, feel sleepy during the day, or brain fog, and your watch asks your SpO2 is good all night you might want to get a dedicated pulse oximeter to screen yourself.
How these devices actually work
Devices are broken into transmissive and reflective. The reflective ones shoot light and catch it in the same spot; think of a watch. These are less accurate and have more "noise" in the data.
Below is a picture of one that is transmissive.
Your blood is literally a different color depending on how much oxygen is in it. Oxygen-rich blood is bright red. Oxygen-poor blood is dark purple. That color difference is what these devices measure. So since oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. On the flip, deoxygenated hemoglobin absorbs more red light and lets more infrared light to pass through.
Two beams of light shine through your finger. The sensor measures how much gets through, and also how much is NOT getting through. Do that math thousands of times per second and you get your SpO2.
Okay, what I scored each device on
Here's what a scorecard looks like for each device in the morning after 3 nights.
And remember these calculations are on how close the consumer device aligned with the hospital grade one.
The metrics are:
- ODI 4% and ODI 3% - did it actually catch oxygen drop events, mild and severe
- Time below 90% SpO2 - total time spent in hypoxia
- Time below 88%: A timer counting every second you spent below 88% oxygen.
- Lowest SpO2 of the night - did it capture the actual worst moment
- Signal stability - how often it hugged the Nonin +/- 2% all night
- Bias - is the device consistently reading higher or lower than reality
- 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.
Bias is the sneaky one. A device that always reads 2% higher than your real oxygen feels reassuring but its actively hiding what's happening. I flagged anything meaningfully above zero as "reads high."
Full list of the rankings
Here is a chart of all of them that I could get the raw data from calculated line by line for 3 days each.
Fitment and Artifacts
Annnnd, it should be noted that in order to align second by second, I had to scrub the artifacts; which are codes that all the devices throw when it loses signal. This can be due to fitment and design. Sensors that are not designed well with poor fitment will have a lot more errors.
Here is the error log by percentages that I had to remove in order to evaluate them. This is data tells us how well this device holds on while you flail around at night.
The most surprising things
The most surprising thing? Price does not always equate to better. Something under $100 tracked just as close to the $1,500 one, as devices that cost three or four times as much.
Also, another thing that genuinely caught me off guard, I tested the Lookee Sleep Ring against the Lookee Pro. The Pro version is marketed as the one with PC software access, which is honestly a big reason people pay more for it. Turns out both of them have PC access. Same feature, different price tag. Make of that what you will, but if you're choosing between the two, that is worth knowing before you buy. This was my experience.
Also, something I learned from sleeping for over 400 hours with these devices is that comfort was really important. A little pressure on your finger while your sitting on the couch checking out the device, is not the same as wearing it for 8 hours night after night. A few of the heavier devices or ones that use pressure to stay on your finger really disturbed my sleep and hurt my finger bad.
How to actually use one of these effectively
One, the more nights of data you collect the clearer your picture gets. One night tells you almost nothing. A month of data tells you a lot.
Two, know what these are and what they are not. These are great for "screening", not diagnosing. An in lab sleep study can run you 10k+, you can buy one of these for a few hundred bucks. After wearing it for a few weeks, go see a doctor if you are experiencing symptoms and seeing consistently more than 10 events an hours. If you are wearing one for weeks and it is reading perfect, and you feel fine, your probably okay.
Under 5 ✅ Normal range. Sleep well.
5 - 15 👀 Mild
15 - 30 ⚠️ Moderate
Over 30 🚨 Severe
They are low cost pre-screening tools. Think of them the way you think of a blood pressure cuff at a pharmacy. It is not a diagnosis. It is a flag.
For my Sleep Apnea suffers, CPAP, COPD, or Sleep Optimizers
Whether you're managing a sleep disorder, on CPAP, dealing with COPD, or just the kind of person who wants to actually know what's happening to your body while you sleep these devices are great for verifying your treatment is actually working , not just assuming it is. A month of overnight data showing your ODI is still elevated is exactly the kind of thing worth bringing to your next appointment.
I put even more time into making a free resource for everyone, which is an interactive database where you can sort and filter by accuracy score, price, form factor, alarm type, FDA clearance, data export format, and more. Continuous Oximeter Database.
I also put together a list of my top picks by use case if you just want someone to cut through it and tell you which one to get: Best Overnight Pulse Oximeters
~Happy to answer questions on any specific device or how the methodology worked. Also still adding devices so if there's something you want tested drop it below! If this genuinely helps some people, my effort will be for naught!😊