I read somewhere that Thomas Edison used to take naps with ball bearings in his hands. At the instant he fell asleep, the bearings rolled out of his hands and hit the floor and woke him up during this transition state.
My farmer friends call it a "spoon nap" sit in a chair holding a spoon, as soon as you fall asleep the spoon drops and you can get back to work. Typically taken directly after a big lunch.
