If the dealer's upcard is an Ace, the player is offered the option of taking Insurance before the dealer checks his 'hole card'.
The player who wishes to take Insurance can bet an amount up to half his original bet. The Insurance bet is placed separately on a special portion of the table, which usually carries the words "Insurance Pays 2:1". The player who is taking Insurance is betting that the dealer was dealt a natural, i.e. a two-card 21 (a blackjack), and this bet by the player pays off 2:1 if it wins. It is called insurance since if the dealer has a blackjack, the bet wins the same amount of the players Blackjack wager, such that if insurance is taken and the player doesn't have blackjack but dealer does, no money is lost. Of course the dealer can end up not having blackjack and the player can still win or lose the blackjack bet.
Insurance is a bad bet for the player who has no knowledge of the hole card because it has a house edge of approximately 7%. Even for the player who has been dealt a natural (a two-card 21) it is unwise to take Insurance. In such a case, the dealer usually asks the player "Even money?" This means that instead of 3:2, the player with the natural accepts to be paid off at 1:1. Thus it is exactly the same thing as buying Insurance, losing the Insurance bet and getting paid 3:2 on the natural.
In casinos where a hole card is dealt, a dealer who is showing a card with a value of Ace or 10 may slide the corner of his or her facedown card over a small mirror or electronic sensor on the tabletop in order to check whether he has a natural. This practice minimizes the risk of inadvertently revealing the hole card, which would give the sharp-eyed player a considerable advantage. In some countries, such as Australia, no face down card is dealt to the dealer until it is his turn to play his hand. This makes the game more complicated since the dealer must keep track of busted split bets since if the dealer ends up drawing a BlackJack the players lose only their original bets and do not lose double or busted split bets.