I was similarly curious; I think your guess about "peeking" is reasonable. Assuming an unsophisticated house that doesn't switch decks, I was also thinking tha

I was similarly curious; I think your guess about "peeking" is reasonable. Assuming an unsophisticated house that doesn't switch decks, I was also thinking that you could even have a tiny bit of isotope-mixed-substance on one finger and "mark" cards that come into your hand on the back in some magnitude. If the detector is near your wrist/in your sleeve you might be able to get some approximate magnitudes of various hands/face down cards in your proximity; or as you say, if the dealer was involved/the one doing the cheat it would be even easier since they could "listen" to the cards as they dealt them. You might not even need it to be directional in this case.