The design is quite good, but it didn't function well. I compared the values to those from a medical grade O2 sensor and the results were sometimes as much as 8% high or low ... which meant there was no value in the reading at all. Product was returned and refunded.

Update Based on Stress Test.
This is my first and only home 02 monitor, and I am very pleased with it.
I had occasion to compare my monitor's 02 readout against medical ones; one time resting and one time during a treadmill stress test:
- resting: My monitor was within 2% of the hospital device's 02 readout, and its readings moved up and down in tandem with the hospital device's. The heart rate measures similarly matched the medical device's readout. This was not a long test, but I was impressed with it.
- in motion (treadmill stress test): The O2 vibe's 02 readout was consistently lower than what the medical device said, by several percent. I had been concerned by the 02 vibe's pattern of 02 drops when I exercied. The stress test showed this was solely due to the 02 vibe not reading well in motion. The 02 vibe's heart rate readout during the stress test was wildly inaccurate. Only occasionally did the 02 vibe's heart rate readout match the medical device's readout.
There is a sensor band that fits around a finger (I put it on my thumb) and a wire (not shown in photo) which connects the sensor to the device.
Take away from the above: I have full faith in the 02 vibe's readouts for sleep, not at all for activity.
It is great for night use. The sensor band has a vibrator built in that will go off if your 02 level drops too much (the threshold adjustable in the device's app). That vibrator was enough to gently wake me to roll over, without waking me all the way up.
The device's readings easily download to my IPad via blue tooth. The readouts in the app are fairly basic, but tell you what you need to know about 02 levels, drops, and heart rate during each session. The app also lets you adjust the threshold for the vibration/alert for low 02 levels.
I've also used the device while bike riding, with the device in day mode. Again, each session can be downloaded to an app to see the full readout of 02 levels and heart rates over the course of the session.
I find the device goes well over 8 hours in night mode (no display showing). I've used it up to three hours in day mode and always had plenty of power left.
One of the only two areas for improvement on the device is that its readout (always on in day/activity mode) is not quite bright enough to read in sunny conditions. The second area for improvement of this device is the band closure. It is clumsy and hard to do yourself. Further, I've had it get pulled open at night when caught on the end of a pillow case or sheet. I don't see why they just didn't use a standard watch band type closure, which would be easier to use and adjust and would hold it more securely.
In all, I would buy this again.

I came very close to giving this 5 stars. I would have given it 4.5 if I could. Major factors in my rating are 1) it works as indicated, customer support is exceptional, the user interface could be better, not completely reliable during exercise (I know it is not expected to work during vigorous exercise), the App doesn't work when location services are disabled on Android.

I had an issue out of the box where it would not connect via Bluetooth to my phone (or several phones for that matter). I emailed customer support, and they responded over the weekend to help. We did a manual FW upgrade and still no connection. We then figured out that in order for the O2 Vibe App to connect to Bluetooth, Location services must be enabled on the phone or the Bluetooth connection is never found by the App. Now it connects via bluetooth very reliably.

Positives
As a sleep monitor it works very well. The band and thumb sensor are comfortable, and do not wake me up at night like other finger sensors that I have used. The pulse and O2 readings appear accurate - as compared to the other two devices I have that have pulse and O2. The graphics on the app show data history and are very readable for me. It works for very light exercise. Battery life is as advertised or slightly better - I can get over 12 hours of monitor time on a charge.

Negatives
The app requires location services to be enabled for Bluetooth connection. The device works during moderate exercise, but it is not always completely reliable (during a very fast walk - ~4 MPH - it does not seem to reliably show pulse and SPO2 the entire time, but will display when holding arm and hand very still.

Other comments
Data download (from device to phone) is slower than I expected, but it is still only a couple minutes each morning. What would have caused me to give 5 starts are 1) App did not require location services, 2) worked better during a fast walk

This device is actually amazing and I would highly recommend it for anyone who wants to monitor their SpO2 levels and heart rate. I'd give it five stars for innovation and design, but Iit does have a few drawbacks that could be easily fixed.

First the pros: it is the only thing at this price point that will monitor your SpO2 and alert you when it drops below whatever setting you input (say, 85 %). Other such monitors are bigger and cost hundreds if not thousands of dollars. It records your heart rate and SpO2 all night (or all day) long and then synchs to your smartphone to give you a full read-out and record if your heart rate and Oxygen. I've attached a screen shot. I love this feature. And, as described, it does indeed vibrate to alert you or wake you if your O2 drops below a pre-set level (you set the level on your phone).

Now the cons: First, the internal battery only lasts about 9 hours. If you sleep longer than that, it will run out. I think they could easily have put in a slightly larger battery. The numbers on the read-out could be slightly larger, too.

But overall it is a great device. Nothing else on the market like it that I know of at this price point.

UPDATE: It turns out I had a faulty sensor. The manufacturer sent me a replacement without any fuss and the item works great now and I have been using it nightly and have decided to keep it. Excellent Customer Service.

THIS IS THE OLD REVIEW:
I would give this 5-stars if it were not for the following:
(1) It stopped connecting to the Droid App. Not sure why, but it seems that I may have to uninstall then re-install the App for this system to once again work - maybe. Which means I will probably lose any previous monitoring results.
(2) The exported image does not include the SpO2 information for some reason (see included image). I have exported the results more than a dozen times with the same results.
(3) The product's control does not actually allow the user to cycle through all the information that is supposedly available.
(4) The documentation (IE: "Quick Start Guide") is missing a lot of instructions on how to do something.