It works for any 50/50 bet ...
... but you have to win before you hit the ceiling.

If you had bet red, black, red, black and kept doubling each time, you would always win your initial stake in the end.

However, on a losing streak, each time your chance of continuing your losing streak halves (i.e. on each red/black or coin toss), the cost of your staying in the game also doubles. You therefore have to have (and be able to bet) many times your anticipated profit to be "sure" you won't lose, 'cos when you do lose you will lose big (you'll lose all of your money or all of the table-limit). In a real casino the table limits will stop you reaching the point where you are pretty certain of not losing and I think they will throw out anyone with an obvious "system" in any case.

Edit - the "extra" numbers in roulette add an additional probability of a loss as those above point out, but even on a coin toss you need a very high earnings to limit ratio.
( Ugi , it's a game of give and cake, Fri 8 May 2009, 16:15, Reply)