Casinos have implemented many techniques and countermeasures to minimize the effect of card counters.
Harassment. The casino could lightly harass counters by talking to them and trying to distract them from keeping the count, or harass them more aggressively by making threats.
Decreasing deck penetration. This means dealing out fewer of the decks in the shoe than they would like. For example, instead of dealing out 5 out of the 6 decks, the casino might deal out only 3 of the decks. Casinos are usually hesitant to do this since the frequent dealing stalls the game and lowers the overall profits of the table. To solve the problem, some casinos use automatic shuffling machines Continuous Shuffle Machines (CSMs), which allow the cards to be shuffled without interrupting the game. It should be kept in mind that when playing online blackjack at sites like Bodog then the software has the ability to shuffle at any time without slowing down the game.
Preferential shuffling. This means that the shoe is shuffled when the count gets high.
Card-counter identification. By using books of photos and facial-recognition technologies, a casino can spot card counters who have been flagged before.
Shuffling when a player increases their wager. Since a large bet spread is the single biggest sign of card counting, the casino could choose that as an indicator to shuffle the shoe.
Changing the rules or table stakes. A casino can make the rules to make the game unbeatable even to card counters or they could make the table stakes so low that a successful counter won't make enough per hour for counting to be worthwhile.
Flat betting a player. By making a player constantly bet the same amount throughout a shoe, a player cannot take advantage of favorable counts.
Prohibiting mid-shoe entry. This keeps players from back-counting.
Computer analysis To try to spot playing behavior indicative of card counting; early counter-strategies featured dealers learning to count the cards.
cwm628 on March 3, 2010