Posts tagged: Ppg

14 posts found

A medical sleep study room with monitoring equipment and sensors, the gold standard for measuring sleep stages that smart rings attempt to approximate

How Smart Rings Calculate Sleep Stages (and Why They're Mostly Guessing)

Your smart ring does not measure sleep stages. It measures heart rate and motion, then guesses. Here's how the guess works, why the industry pretends otherwise, and why Pulsyn tells you the truth.

James Hoffmann

Jun 8, 2026 14 min read

A person breathing deeply during meditation, illustrating the physical act of respiration that smart rings never actually measure

OuraWhoopAccuracy

How Smart Rings Guess Your Breathing Rate (and Why the Number Is Mostly Fiction)

Your smart ring does not count your breaths. It counts the ripples that breathing leaves on your heart rate, then runs statistics to guess how many times you inhaled. The method is real. The precision is not.

James Hoffmann

Jun 8, 2026 11 min read

A runner on a track at sunset, the exact scenario where smart ring heart rate tracking fails due to finger blood flow physics

AccuracyExerciseFitness Tracking

Why Smart Rings Are Bad at Workout Tracking, and the Physics of Finger Blood Flow

Smart rings promise workout tracking, but the physics of finger blood flow makes PPG nearly useless during exercise. Here is why the heart rate data is often fabricated, and why Pulsyn does not pretend otherwise.

James Hoffmann

Jun 3, 2026 13 min read

A close-up of an LED optical sensor circuit board used in biometric wearable devices

PpgHeart RateSensors

How Photoplethysmography Actually Works in a Smart Ring

Most smart rings shine light into your finger and count the bounces. The ones that do it well sample at 100 Hz or higher, use green and infrared LEDs in a specific geometry, and process the signal before it ever reaches a server.

James Hoffmann

Jun 1, 2026 13 min read

Macro photograph of finger skin showing the dense capillary network near the surface. The biological reason transmissive PPG works better at the fingertip than the wrist.

SleepPpgForm Factor

Why the Smart Ring Form Factor Is Better for Sleep Than the Wrist: A Physics Argument

The wrist is the worst place to measure heart rate during sleep. It is too thick for transmissive PPG, too prone to motion artifact, and too thermally unstable. The finger wins on every metric that matters for overnight biometrics.

James Hoffmann

May 29, 2026 13 min read