Posts tagged: Sensors

5 posts found

An ECG waveform diagram showing the difference between normal sinus rhythm and the chaotic irregular pattern of atrial fibrillation, illustrating what smart rings try to detect with PPG sensors

Your Smart Ring's AFib Detection Is Not Medical Grade. Here Is What It Actually Measures.

Smart rings use PPG sensors to detect patterns that may suggest atrial fibrillation. But PPG-based AFib detection is not medical-grade diagnosis. Here is how it works, what the accuracy actually looks like, and why the Circular Ring 2 with real ECG is the exception.

James Hoffmann

Jun 26, 2026 1 min read

An oscilloscope display showing a clean waveform, representing the textbook PPG signal that smart rings almost never actually capture during motion

PpgHeart RateSensors

What Your Smart Ring's Heart Rate Data Looks Like After You Move: Motion Artifacts, Adaptive Filters, and the Signal You Never See

Your smart ring's PPG sensor produces clean heart rate data roughly 40 percent of the time. The other 60 percent is a signal that has been through an adaptive filter, and what comes out is a reconstruction. Here is what actually happens inside the chip when you wave your hand.

James Hoffmann

Jun 18, 2026 1 min read

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

PpgHeart RateMedical Devices

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 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

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

Skin TemperatureSleep ScienceSensors

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