Wearables & Tracking
Which numbers on your wrist mean something, and which are confident guesses.
Wearables are excellent at some measurements, mediocre at others, and presented with uniform confidence throughout. That mismatch is the problem: a device that estimates your heart rate well and your calorie burn badly shows you both in the same font.
These pages sort the outputs by how well they validate against laboratory reference methods, and explain what each is actually useful for. Our own calculators are estimates too, and we say where they're weakest.
Guides
- Why Your Watch's Calorie Count Is Wrong
Wrist devices measure heart rate reasonably well and estimate energy expenditure badly. Validation studies have been consistent about this for years.
- How Accurate Are Sleep Trackers?
Total sleep time: reasonable. Sleep stages: the least reliable thing they show you, and the number people fixate on.
- HRV and Readiness Scores: What They're Worth
Heart rate variability is a real physiological signal. A single proprietary readiness number is a long way downstream of it.