Heart rate variability: what your watch is measuring
HRV is the tiny variation in timing between heartbeats. Wearables use it as a signal of recovery and stress. Here is how to read the number.
Heart health tech
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How smartwatch blood oxygen readings work, and where they fall short
A watch estimates blood oxygen by shining red and infrared light into your wrist. The method is sound and the wrist is a hard place to do it.
VO2 max on your watch: how it is estimated
The lab test needs a mask and a treadmill. Your watch works it out from pace and heart rate. Here is what the estimate is good for.
Google's watches will report blood pressure and insulin resistance trends
Health Guardian, announced in August 2026, estimates the trends from existing sensors. It does not measure either one.
Pixel Watch 5 added a feature that calls for help when breathing fails
Google's $399 watch, announced in August 2026, watches for severe drops in blood oxygen. The feature launched in Europe first.
What the FDA's 2026 wellness rules let your wearable tell you
A January guidance opened the door for watches and rings to estimate blood pressure and glucose without FDA review, as long as they stay away from diagnosis.
Apple Watch hypertension alerts: what the FDA cleared in 2025
The feature does not measure blood pressure. It watches a month of heart sensor data for a pattern and tells you to get checked.
The FDA's warning to Whoop over blood pressure estimates
In July 2025 the agency said a wearable that estimates blood pressure is a medical device, whatever the disclaimer says. Whoop disagreed.
A cuffless blood pressure band was cleared for sale without a prescription
In July 2025 the FDA cleared Aktiia's wrist-worn Hilo band, days before warning Whoop over a similar feature it had not reviewed.
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