Card counting is one of the few advantage plays that actually works. A skilled counter can flip the house edge in blackjack from minus 0.5 percent to plus 1.5 percent. That's why casinos take it seriously. They can't legally arrest counters (counting is not illegal), but they can ban you, back you off, or shuffle the deck early. And they catch most counters within an hour. Here's how.
The first signal: the bet spread. Counters bet small when the deck is bad and big when it's good. That's the entire edge. Pit bosses are trained to watch for 'bet correlation': a player whose bet size jumps from 25 to 200 dollars and back without obvious wins or losses. Modern surveillance software automates this. A camera tracks every bet and flags spreads above 4 to 1 or 8 to 1 for review.
The second signal: the playing decisions. Counters deviate from basic strategy in specific situations: taking insurance with a high count, hitting 16 versus 10 with a low count, doubling 9 versus 2 with a high count. Each of these 'index plays' is harmless on its own but becomes a signature when grouped together. Pit bosses don't need to memorize the whole index. They just need to notice 'this player is making weird moves at exactly the right times.'
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The third signal: focus and demeanor. Recreational players talk, joke, and lose track of the cards. Counters watch every card that hits the felt, even the cards from other players' hands. They sit at third base (the last seat) so they see everything before deciding. They rarely drink. They tip moderately to blend in. Surveillance teams call this 'the counter look' and it's surprisingly easy to spot once you know what you're watching for.
The technology layer. Major casinos now use software that does this automatically. Systems like Bloodhound, Angel Eye, and SmartShoe track every card and bet in real time, calculate the running count, and alert surveillance when a player's bet pattern correlates with the count. The MIT blackjack team got caught largely by these systems in the 1990s. Modern versions catch counters faster than any human pit boss.
The 'heat' timeline. A new counter typically gets noticed within 30 to 60 minutes. The pit boss starts paying attention. The shoe gets shuffled early to break the count. If the counter persists, a floor manager comes over and 'introduces themselves' (a polite warning). If the counter doesn't slow down, they get a tap on the shoulder: 'We'd prefer if you stuck to other games.' That's the back-off. Refuse to leave and you can be trespassed and added to a database of banned players (the famous Griffin Book, now replaced by digital systems).
The famous catches. The MIT blackjack team won an estimated 5 to 10 million dollars across multiple casinos before private investigators traced their movements via surveillance footage and bank records. Don Johnson beat Atlantic City for 15 million dollars in 2011, but only after negotiating special rules and bet limits in advance. Even Phil Ivey, one of the best advantage players ever, was caught and sued at Crockfords London after his edge-sorting baccarat session.
What this means for you. If you're learning to count cards, three rules matter. First, your bet spread is the loudest signal; keep it small (2 to 1 or 3 to 1) at smaller casinos, never push 8 to 1 unless you're moving fast. Second, blend in with recreational players, drink water, joke around, lose a few hands on purpose. Third, don't get greedy at one casino. The MIT team rotated through dozens of casinos for a reason. The moment you turn into a regular winner at a single property, the surveillance team will find you.