From tracking heart rate to monitoring sleep, wearable devices provide valuable insights into your health and well-being. But when it comes to accuracy, where you wear your tracker matters.
While wrist-worn devices may have been first to market and are more recognized, a growing body of evidence suggests that finger-worn wearables, such as Oura Ring, are likely to offer superior performance and wearability.
« There is increasing evidence that the finger form factor offers a significant advantage in the robustness of the signal and overall device performance, making it the preferred site for high-fidelity physiological monitoring,” says Dr. Massimiliano de Zambotti, PhD, sleep researcher and staff research scientist at Oura.
Physiological Advantages: Why the Finger Has the Upper Hand
“One of the key reasons for the effectiveness of finger-based physiological measurements is the rich vasculature of the skin at the finger, which provides strong and stable signals for various biometric measurements,” Dr. de Zambotti says.
Compared to other body locations for wearable devices, the finger has advantages in terms of physiology and anatomy, including:
Rich blood flow: The finger’s rich blood flow provides a clearer, stronger photoplethysmography (PPG) signal than the wrist, which is subject to more movement and typically has more body hair, which can interfere with measurements.
Higher vascular density: The finger has a dense capillary network and multiple small arteries (digital arteries) near the surface, making it ideal for detecting blood volume changes.
Consistent skin thickness and pigmentation: The palmar side of the finger may offer an advantage both in terms of skin thickness and more consistent pigmentation.
What Is PPG?Oura Ring measures 40+ biometrics, including heart rate, heart rate variability (HRV), temperature trends, and sleep. One of the methods Oura uses to measure these metrics is called photoplethysmography (PPG), which measures the volumetric changes in your arteries using light reflection. The PPG signal is an optical measurement of the arterial pulse wave—i.e. the wave generated when blood is ejected from the heart, temporarily increasing arterial pressure and causing vessel expansion and contraction. PPG works by shining a light on your finger and capturing the changes in light reflected back from the red blood cells in your arteries. Research has shown that this signal contains a wealth of information on the heart, blood vessels, breathing, and autonomic nervous system, and it provides the basis for Oura’s Cardiovascular Age estimate. |
Cutting Out the Noise: A Clearer PPG Signal
“A clear PPG signal is critical for the analysis of its waveform characteristics and derived metrics,” Dr. de Zambotti says.The finger’s unique anatomy is able to provide a clearer PPG signal relative to other locations for wearable devices, as various studies have shown.
- A 2019 study compared PPG measurements from six different body sites (finger, wrist under, wrist upper, arm, earlobe, and forehead) and found that signals from the finger achieved the highest percentage of analyzable waveforms.
- A 2021 study suggests that PPG signals from the finger were generally clearer and easier to analyze than the signals from the wrist. Specifically, the wrist signals had missing or unclear « landmarks » more often than the finger signals—making it harder to get a clear and complete picture of blood flow from the wrist than from the finger.
- Multiple studies, such as Longmore et al. 2019, suggested that for the most clinically relevant measures, i.e., PPG-derived heart rate (HR) and blood oxygen saturation (SpO2), the finger location proven to be overall superior to wrist, as well as to other body locations.
Plus, the finger has traditionally served as the gold-standard site for clinical applications, such as measuring blood oxygen saturation (SpO2), notes Dr. de Zambotti. Clinical polysomnographic tests designed to evaluate the presence and severity of sleep apnea also include finger pulse oximetry.
Clearer PPG Signals Mean More Accurate Data
Factoring in the finger’s physiology plus the clearer PPG signals, a finger-worn device such as Oura Ring is able to provide highly accurate biometrics. Additionally, Oura’s proprietary software and best-in-class algorithms add further fidelity when analyzing metrics such as heart rate and sleep, as multiple peer-reviewed studies have shown.
- Researchers found “very high agreement” between the Oura Ring and the gold-standard ECG measurement. The Oura Ring performed near-perfect for resting heart rate and extremely high for heart rate variability when compared to a medical-grade ECG device.
- A 2021 study found Oura’s sleep staging algorithm achieves 79% agreement with gold-standard polysomnography (PSG) for classifying the four stages of sleep (wake, light, deep, and rapid eye movement (REM) sleep).
- In 2024, researchers at the Brigham and Women’s Hospital (BWH) evaluated the accuracy of sleep-staging algorithms in three consumer wearable devices—Oura Ring, Fitbit Sense, and Apple Watch—against gold-standard polysomnography. The results of their study found that Oura Ring was the most accurate sleep tracker in four-stage sleep classification: 5% higher than Apple Watch and 10% higher than Fitbit, adjusted for chance and compared to gold standard assessments
The Oura Advantage
Weighing only 3.3 to 5.2 grams (depending on size), Oura Ring 4 is light and unobtrusive. With barely noticeable recessed sensors at a height of 0.3mm and a fully titanium inner and outer coating, Oura Ring 4 provides all-day and all-night comfort—with no bright screens or notifications to disrupt your sleep.
With six finishes to choose from to suit your style, Oura Ring 4 is also fashionable—not to mention functional. Ready to give it a try?