Brain Waves - Magic Trick

You hand an ordinary deck of playing cards to a spectator for examination. He can shuffle the deck, if he wants. Then you slowly go through the face down cards and tell the spectator to say ‚Stop‘ five times, so that five arbitrary cards are chosen. (This is a truely free selection.) You tell the spectator that you have to look at the cards carfully and memorize them.
Then you hand the iPhone over to the spectator and tell him to open the Brain Waves app. You reveal four of the cards one by one and the spectator enters them in the app by specifying suit and rank. When the cards have been entered, you tell the spectator that you have to concentrate, so that the phone can pick up your brain waves.
Now you ask the spectator to shake the phone. After the shake, the back of a single playing card is shown in the app. You ask the spectator to tap on the card and it flips over.
Now you reveal that this card is the same as the fifth card that the spectator had chosen!
The app comes with a detailed description on how the effect works and how it can be performed.
Optimized for the systemwide light and dark mode (see screenshots).