Card counters in Blackjack can often be detected through their betting and playing behavior. One of the most common signs is a fluctuation in bet sizes, where players increase their bets when the deck is favorable and decrease them when it's not. They may also deviate from basic strategy, making decisions that seem out of place, like standing on 16 against a dealer’s 10, based on the count. A card counter tends to be more focused on the game, paying close attention to the cards dealt and the dealer's upcard. Additionally, they may adjust their play speed, sometimes pausing to calculate the count, and might exhibit signs of nervousness or hesitation if they feel they are being watched. Card counters also tend to move between tables or casinos to avoid detection, and they may manipulate chips when adjusting their bets. Casinos counter these tactics with surveillance, using multiple decks or continuous shuffling machines, and training staff to spot suspicious behaviors.