Wearables and Health Trackers: What They Measure and How Accurate They Are

Quick answer

Consumer wearables are reasonably good at some measures, such as heart rate and steps, and poor at others, such as calories burned. They are not diagnostic tools. Labels used: established, promising but limited, mixed, insufficient evidence, marketing claim. For longevity context see wearables and sleep tracking for longevity.

Wearables: what they measure and how accurate they are

Blood sugar from a watch or ring. The FDA says: do not buy or use smartwatches or smart rings that claim to measure blood glucose, and that it has not authorized, cleared or approved any such device that works without piercing the skin. [7] Inaccurate readings can cause dosing errors in diabetes care, with low glucose that can be fatal. [7]

Inflammation and illness. Wearable heart-rate variability is only an exploratory measure for inflammation, according to a 2026 systematic review; clinical usefulness is limited by inconsistent results. [8]

What wearables cannot do

A device reading is not a diagnosis. Sleep trackers are not a substitute for sleep lab testing. [9] Most trials tested specific models, and new versions arrive faster than research does. A reading that looks alarming should be discussed with a clinician rather than acted on alone.

Mental cost and who should be careful

A 2026 neurology review notes that heightened anxiety remains an important unintended consequence of wearables in people with neurologic conditions. [10] Clinicians have described people chasing perfect sleep data. [11] If tracking feeds worry, perfectionism or disordered eating, pause it; see nutrition tracking. People with heart rhythm problems or diabetes should use medical-grade devices recommended by their care team.

How to evaluate a wearable claim

Ask what was measured, in whom, compared with what gold standard, and whether the study was independent. See how to evaluate a biohack and sleep optimization.