Sleep trackers — wearable devices that monitor all your vitals — provide detailed summaries of your sleep cycle so you know how many hours of REM ... In the Oura app, under the "My Health ...

The brain waves of a person in REM sleep look very similar to those of a person who is awake, which is why some sleep-tracking apps show blocks of REM as occurring near the top of the graph ...

REM), heart rate variability and dipping, blood oxygen levels, respiratory rate, external environmental audio, and even body ...