Oura Ring 5 shows high heart rate accuracy but lags in sleep tracking

The Oura Ring 5 features a streamlined, lightweight design intended for long-term comfort and daily wear. While the device demonstrates exceptional accuracy in nighttime heart rate and heart rate variability (HRV) tracking—comparable to ECG chest straps—it shows limitations in other areas. Specifically, sleep stage tracking, particularly REM sleep detection, has seen a decline in accuracy compared to the previous Oura Ring 4, trailing behind competitors such as Fitbit and Whoop.

Fitness trackers generally rely on sensors like photoplethysmography (PPG) to monitor heart rate by measuring light reflection from blood flow in capillaries. Because raw sensor data is often noisy due to motion, skin color, or device pressure, manufacturers use complex signal processing and accelerometers to filter out artifacts and convert raw signals into actionable health insights like sleep and readiness scores.