Betting systems in the game of blackjack, roulette and craps are usually not considered to be very effective in increasing the player’s chances of winning.  The house advantage is the same for each kind of bet, except the Five bet in American Roulette and that has a large house advantage.  There is no method that can lower that house advantage so there is no method that can result in a winning methodology that is consistent. In spite of this, people keep trying to develop a method to beat the wheel.

The D’Alembert system was devised specifically for the game of poker, bingo and roulette.  The system is used in even money betting situations when plays bingo or else.  It is a simple strategy.  When the player wins he decreases his bet by one chip (or unit) and when he loses he increases his bet by one chip. This method is based on probability.  In say one thousand spins, half of the outcomes should be red (or even or high) and half should be black (or odd or low).  Therefore, the player should theoretically win half of his bets.  This system is usually used to protect winnings that were won previously.  The problem is that the fifty-fifty outcome is over a large number of spins.  Unless the player plays that long run number of spins, there is no guarantee that he will win.  And there is still the house advantage that is operative. If your purpose is to protect your winnings, why not just leave the table with those winnings?