Pete Najarian, co-founder of OptionMonster.NEW YORK ( TheStreet) -- Traders turned bullish on Bank of America ( BAC) and Citigroup ( C) on Monday. OptionMonster's systems Monday detected early buying in Bank of America's Weekly 9 calls, which expire this Friday, for 17 cents and 18 cents. Traders then made additional short-term bets a little while later in Citigroup, buying its Weekly 34 calls for 37 cents to 41 cents. Calls lock in the price investors must pay for the stock, so they can generate major leverage in a hurry if these banks move in the right direction. But if the stocks don't rally, those options will expire worthless. Citigroup fell 2.36% to $33.97 Monday, coming off its session lows as the options were bought. Total calls in the name outnumbered puts by 77,000 to 53,000. Bank of America attempted to rebound but finished near its lows, down 3.25% to $8.93. Najarian owns C shares and BAC calls.