GoKawiilFor as long as I've been covering health and fitness trackers, which is basically since the dawn of the category, they've been synonymous with the wrist: Apple Watch, Fitbit, Garmin, Samsung Galaxy Watch. Sure, exceptions exist, but most wearables are designed for the wrist, likely for the same reason the pocket watch moved there a century ago: convenience. Nobody really questioned it, least of all me.
That is, until I reviewed the Whoop band.
The Whoop appeared like any other wrist tracker, except it had no screen, and its sensor could be placed in different locations to passively measure health data. After realizing the arm band was more comfortable for sleep, I started exploring other ways to wear it. The same sensor can be worn on your bicep, tucked into a sports bra or even clipped into underwear.
It was the Whoop thong (yes, this is a thing) that really sent me into detective mode. The idea that a sensor in your underwear could track the same metrics and with the same level of accuracy as one on your wrist felt like a stretch. The fact that Whoop sells all these options on its website suggests it stands behind the data, but I was skeptical.
Today's wearables aren't just counting steps. They're flagging signs of atrial fibrillation, detecting sleep apnea, estimating blood pressure trends, tracking hormonal patterns and more. Wearables are not medical-grade devices and shouldn't replace professional expertise or treatment. But the results are edging closer and closer to clinical-grade precision.
Devices are also moving off the wrist entirely. The Oura Ring and other smart rings track vitals from your finger, and earbuds (like Apple's AirPods Pro 3) have added heart rate sensors. Companies like Lumia are also experimenting with sensors embedded in earrings.
As someone who trains regularly and depends on this data to guide my workouts and recovery, I wanted to know whether placement matters and, if so, by how much. So I went to the researchers. I found that sensor placement does affect accuracy, but it's not the only factor. Fit, consistency and, most importantly, the specific metric you're tracking can make an even bigger difference than wearable placement alone.
How wearables read your body
To understand why the placement of a wearable matters, it helps to know how these sensors work. Most of these devices use optical sensors called photoplethysmography, or PPG, a light-based technology that measures blood flow under your skin. When your heart beats, blood surges into your vessels and absorbs more light. Between beats, less blood means more light bounces back to the sensor. That fluctuation is how your watch detects your heart rate, blood oxygen levels and more.
Your smartwatch detects your heart rate by shining green light into your skin and measuring how much bounces back. Viva Tung/CNET
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