This is NOT a real lie detector, just a magic trick to amuse your friends.
EFFECT: The spectator takes a card from a deck, and hides it so nobody can see it. Then you introduce the Lie Detector app, which seemingly can decide if someone was telling the truth or was lying (this is NOT true, as this app is just a fake lie detector). The spectator can hold the phone (or tablet) in their hands, you never touch the device after starting the app! The spectator says something about their card - they can tell the truth or lie ("it's a black card", "it's a number card" etc.), and then they put their finger on the screen. The Lie Detector will decide if they were lying or not. After a couple of statements, you can successfully reveal the spectator's card.
METHOD: You will find detailed instructions inside the app. Please read it before you rate the app!!!