Lucid dream induction is possible by the use of a physical device. The general principle works by taking advantage of the natural phenomenon of incorporating external stimuli into one’s dreams. Usually a device is worn while sleeping that can detect when the sleeper enters a REM phase and triggers a noise and/or flashing lights with the goal of these stimuli being incorporated into the dreamer’s dream. For example flashing lights might be translated to a car’s headlights in a dream.

Another induction stimulus is vibration. A small vibrator placed on the hand, arm or ankle and triggered by REM activity, or a timer, can also serve as a cue to trigger a lucid dream. Additional techniques include reality tests (as below) practiced in waking life can lead to a test taking place within a dream, leading to the realization that one is dreaming or meditation.[citation needed] hypnotic suggestion may help a person to achieve lucidity. Michael Katz referenced using simple hypnotic induction for the purpose of initiating lucid dreams in his introduction to the first edition of the book Dream Yoga and the Practice of Natural Light. From the early 1980s, he went on to use this “guided nap” technique during dream yoga and lucid dream training. He conducts training internationally and maintains an archive of examples.