Oura, maker of the popular smart ring, is facing a class-action lawsuit alleging it misled customers by claiming the device can accurately track sleep stages such as REM, deep and light sleep. The complaint argues this is impossible because the ring cannot directly measure brain waves, and describes its AI-based sleep-stage estimates as no better than a coin flip. The Verge's wearables columnist argues the claim misunderstands how all wearables work, since none measure anything directly beyond motion, and Oura's software instead infers sleep stages from indirect signals.

The columnist notes that heart rate, body temperature and muscle activity all change measurably across sleep stages, giving devices like the Oura Ring legitimate physiological cues to work from, and that Oura has published peer-reviewed validation studies and a supportive op-ed from a sleep researcher in rebuttal. Independent reviews generally find wearables reliable at detecting sleep and wake times, though accuracy for individual sleep stages varies by algorithm and can be thrown off by factors such as sleep position or low battery. The author's broader point is that accuracy debates miss the purpose of such devices, which are meant to reveal long-term lifestyle trends rather than serve as precise diagnostic tools.