Lucidly

Lucidly is built around a simple premise: lucid dreaming gets much easier if something reliably tells you that you are in REM sleep right now. The app collects heart-rate and other health readings through Apple Watch overnight, feeds them into artificial neural networks, and fires a subtle haptic (and optionally acoustic) signal when it believes you have entered Rapid Eye Movement. You then either notice the cue inside the dream or wake briefly and re-enter REM using a technique of your choice.

Because every sleeper differs, Lucidly deliberately exposes the 'guts' of its machine learning. You can tune detection thresholds, alarm durations and haptic intensity, and review how your results change over time. That customisation matters, since the developers are upfront that REM prediction accuracy varies from person to person and from night to night, and that feedback can occasionally land in deep or light sleep rather than in a dream.

Lucidly requires an Apple Watch as well as an iOS device. There is no account and no registration, and subscriptions can be cancelled at any time. A seven-day promotional trial is offered so you can test detection quality on your own sleep before paying, and access continues until the end of the paid period after cancellation.