Posts tagged: Wearables

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A close-up of a heart rate monitor sensor on a finger, showing the pulse reading in real time

On Device Ai · Wearables · Hrv

How Pulsyn Calculates Resting Heart Rate (and Why Your Current Number Is Probably Wrong)

Most wearables report resting heart rate as the lowest heart rate they can find, usually during sleep. The clinical definition is different. Pulsyn measures it during motionless awake periods, and the gap between the two definitions is often 10 to 15 beats per minute.

James Hoffmann

Jun 3, 2026 13 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

Activity & Movement · Wearables · Hrv

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 neon-lit circuit board representing the internal hardware of wearable devices that users are reverse engineering to reclaim their health data

Wearables · How It Works

Why People Are Cracking Their Oura Rings

A Reddit post called Cracked Oura hit 769 upvotes by showing how to bypass Oura's mandatory subscription using raw BLE data. The thread turned into a product support forum for a product Oura refused to build.

James Hoffmann

Jun 2, 2026 14 min read

A hotel room at night with an unmade bed, representing the unfamiliar environment where the first night effect occurs and sleep trackers get confused

Sleep · Research, Explained · Wearables

How Traveling Breaks Your Sleep Tracker (and Why the First Night Effect Is Real)

The first night effect is a documented neurological phenomenon where half your brain stays awake in unfamiliar environments. Most wearables treat this as a bad night and tank your score. They should be treating it as a different kind of night entirely.

James Hoffmann

Jun 1, 2026 11 min read

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

Wearables · Hrv

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 person walking on a forest path, the kind of everyday movement that step counters attempt to measure

Activity & Movement · Wearables

What Your Step Count Actually Means and Why 10,000 Is a Marketing Number

The 10,000 step goal was invented in 1965 by a Japanese pedometer company. It had no clinical basis then and has only weak evidence now. Most wearables count steps using flawed accelerometer guesswork, which means your 8,000 step day and your friend's 8,000 step day are not the same health outcome.

James Hoffmann

May 31, 2026 13 min read

A medical stethoscope on a desk with clinical documents, representing the regulatory gap between wellness devices and validated medical equipment

Research, Explained · Wearables

Your Smart Ring Is a Wellness Device, Not a Medical Device. Here's What That Actually Means.

The FDA's 19-page general wellness policy lets smart ring companies skip clinical validation entirely. Every wearable you have heard of lives inside that loophole. The difference between wellness and medical is not a matter of degree. It is a matter of whether anyone tested the accuracy before it shipped.

James Hoffmann

May 31, 2026 12 min read

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

Sleep · Privacy · On Device Ai

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

A person running on a treadmill in a lab setting, the exact environment where Stanford tested fitness trackers against clinical calorimeters

Activity & Movement · Research, Explained · Wearables

Why Your Wearable's Calorie Count Is Wrong by 27 to 93 Percent

A Stanford study tested seven fitness trackers against clinical instruments. Heart rate was accurate. Energy expenditure was off by 27 to 93 percent on every device. The calorie number on your screen is not a measurement. It is a guess.

James Hoffmann

May 30, 2026 15 min read