Posts tagged: Accuracy

13 posts found

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

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

A data visualization dashboard showing algorithmic learning patterns, representing how smart rings build personalized baselines over time

BaselineCalibrationSleep Tracking

How Smart Rings Learn Your Body (and Why the First Two Weeks Matter)

Your smart ring is guessing for the first two weeks. Every sleep score and recovery metric is built on population averages until the algorithm learns what normal looks like for you. Most companies do not tell you this clearly. Pulsyn does.

James Hoffmann

May 30, 2026 12 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

A medical pulse oximeter clipped to a fingertip, using transmissive light technology that consumer smart rings cannot replicate

Spo2Pulse OximetryFda

Why Your Smart Ring SpO2 Reading Is Probably a Guess

Consumer wearables run reflective PPG on body parts never designed for it. The FDA has scrutinized these monitors since 2022 for systematic bias. Smart rings compound the problem with clamp pressure and unvalidated algorithms.

James Hoffmann

May 28, 2026 11 min read