1.) The signal to trigger lucidity is wakefulness. When awoken from within a dream, the trick is to not move as the sensitive build-up of micro-doses of neurotransmitters – perchance DMT, gets washed away when you toss or turn.
2.) The easiest way to detect the dream state is to watch for eye movements. And the most comfortable way to do this is to have the subject sleep on their side facing a night-vision camera on the night-table.
3.) REM sleep is not equal to dreaming. The REM sleep phase as classified by sleep staging from EEG does not mean that a subject is dreaming. Eye movements are a more reliable indicator that the subject is hallucinating.