You are thinking of Salvador Dali. He would hold a spoon in his hand and rest it above a plate. When he fell asleep the spoon would fall and make a clang with the plate. Jolting him awake again, he would try to recall whatever was happening in his subconscious right before being startled awake and try to express it on canvas.
> He would hold a spoon in his hand and rest it above a plate
I do a variation of that too. And my plate has cereal in it ... The moment I wake up I go: "oh hello, what's that ... breakfast!" - and instantly I'm in a good mood. It's like a form of meditation I call "bowlfullness"
And I do love my lucid dreams, at some points of my life they would ruin my sleep but I found them a good trade off.