Hi Megan

I worked in this field a few years back. Honestly most of these things work
roughly the same so I think the one you will wear and you like the look of
is probably the best.

They all have roughly the same sensors. To detect HRV or VO2 you need to
have A PPG sensor which uses IR light to detect blood flow and oxygenation
through the skin. Most trackers will have this plus an
accelerometer/gyroscope to detect movement and possibly skin temperature
sensors. They’ll all tout their algorithms but they are basically the same
machine learning models. There’s only so much you can do it really comes
down to signal to noise..

The bigger question is where it physically is on your body, because that
impacts the signal quality. You want something that fits snugly to reduce
random moment and poor signal. Step count will always be bad unless the
sensor is on your hip or better your foot. If it’s a wrist band you’ll get
a lot of false counts because you move your arms around a lot. Sleep
staging will also always be iffy because you really need an eeg electrode
on your head to do that. Most of the products do sleep staging by detecting
movement. When you stop moving they say you’re asleep. You can do a bit
more by integrating blood flow and temp or respiration inferred from
movement of to analyze sleep but it’s always going to be a bit dodgy. If
you are lying still with your eyes open it will think you fell asleep
because you aren’t moving. It’s just the wrong signal.

That said these trackers can tell you some interesting things if you take
them with a grain of salt. A product that fits snugly and you like the look
of and will wear is the way to go I think. Also look at the features of the
app and see if you’ll use them. The Oura ring is supposed to be good. It
fits snugly on your finger so gets good signal. It’s classy too.

https://ouraring.com

Probably more information than anyone bargained for …

Good luck!
Rob



On Tue, Jul 29, 2025 at 6:21 PM Debra Daugherty <[email protected]>
wrote:

> I wear a Whoop. Not sure how the price compares to others. As far as I
> know, it's the most accurate for tracking restorative sleep, which is why I
> got it. Apparently it is bad at tracking steps. So it depends on what stats
> matter to you most.
>
> On Tue, Jul 29, 2025, 4:37 PM Megan McCoy <[email protected]>
> wrote:
>
>> Hello,
>> Looking for an affordable wearable device to track VO2, heart rate
>> variability, sleep, etc...  Any recommendations?   And also best place to
>> purchase used or new.
>>
>> TY
>> Meg
>>
>
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