100% impromptu. Can be done with borrowed deck. It's a utility concept that allows you to create your own effects.
Imagine being able to know the chosen card without touching the deck.
The participant can shuffle the deck, take any card, free choice, you don't touch the deck, the card is isolated by the participant and you're able to tell which card it is without touching it.
But the best way to use this method is hidden in a routine, not to find out one selection, but to create something bigger, as you will learn in this project.
Routines included.
Basic to advanced.