Posts tagged: Biometrics

5 posts found

A pregnant woman wearing a smart ring, with abstract biometric data lines flowing around her finger

Your Smart Ring Has No Idea You're Pregnant: How Pregnancy Breaks Every Biometric Algorithm

Pregnancy raises your resting heart rate by 10 to 20 bpm, drops your HRV, raises your temperature, and changes your sleep architecture. Every wearable algorithm trained on non-pregnant baselines gets this wrong. Here is what the data actually looks like.

James Hoffmann

Jun 21, 2026 1 min read

An assortment of prescription medication pills scattered across a surface, representing the medications that alter biometric signals measured by smart rings

BiometricsWearable AccuracyMedication

The Medications That Break Your Smart Ring's Algorithms

Beta-blockers suppress HRV by 30 to 50 percent. SSRIs alter sleep architecture. Antihistamines fragment deep sleep. If you take medication and your smart ring gives you bad scores, the problem might not be your body.

James Hoffmann

Jun 19, 2026 1 min read

Closeup of roasted coffee beans scattered on a white surface, representing the source of caffeine that disrupts wearable biometric readings

PpgHeart RateBiometrics

Why Your Morning Coffee Confuses Your Sleep Tracker: Caffeine, Biometrics, and the False Recovery Signal

Caffeine changes your biometrics in ways that look like recovery to a wearable. Higher HRV, elevated resting heart rate, and altered sleep architecture produce a readiness score that says you are rested while your body metabolizes a stimulant. Here is how the blind spot works and what wearables could do about it.

James Hoffmann

Jun 17, 2026 1 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