Posts tagged: Heart Health & HRV

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A close-up of an ECG monitor screen showing the characteristic electrical waveform of a heartbeat. Smart rings measure something completely different.

Research, Explained · Wearables · Hrv

Why Smart Rings Can't Do ECG

The Apple Watch measures electrical voltage. Every smart ring measures light bouncing off blood. These are two different physical phenomena, and the ring form factor makes ECG impossible with current technology.

James Hoffmann

Jun 10, 2026 13 min read

A close-up of a green LED and photodiode sensor on a small circuit board, the same components found inside every smart ring that claims to monitor your heart rate continuously

Wearables · How It Works · Hrv

The 'Continuous' Heart Rate Lie: Why Your Ring Samples Your Pulse in Bursts, Not Streams

Smart rings claim 'continuous' heart rate monitoring. The physics of photoplethysmography and a 20 milliamp-hour battery make that impossible. Here is the duty cycle nobody talks about, and why Pulsyn shows the gaps instead of hiding them.

James Hoffmann

Jun 9, 2026 11 min read

A blood pressure monitor cuff on a desk, the exact device smart rings would need to replace to measure blood pressure accurately

Wearables · How It Works · Hrv

Why Smart Rings Can't Measure Blood Pressure Yet

Blood pressure is a force measurement, not a volume measurement. A PPG sensor in a smart ring tracks blood volume, not pressure. Here is why that gap cannot be closed with machine learning alone, and why Pulsyn will not ship a blood pressure estimate until the physics actually works.

James Hoffmann

Jun 9, 2026 14 min read

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

On Device Ai · Wearables · Hrv

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 conceptual visualization of stress physiology showing the interconnected nervous system response that wearable devices attempt to measure

Stress · On Device Ai · How It Works

What Goes Into Pulsyn's Stress Score

Most wearables compute a stress score by running your heart rate through a black box. Pulsyn does the same thing, but the weights are public, the math is in the repository, and the app tells you exactly how confident it is. Here is the full breakdown.

James Hoffmann

Jun 4, 2026 13 min read

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 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

Thermal imaging of a human hand showing heat distribution. The kind of raw signal most smart rings average away

Sleep · On Device Ai · Wearables

What Skin Temperature Actually Tells You (And Why Most Rings Get It Wrong)

Skin temperature is a proxy for blood flow, circadian phase, and autonomic tone. Most smart rings average it into a single nightly number. We do not.

James Hoffmann

May 28, 2026 14 min read