Threshold chloride levels for localized corrosion of carbon steel material have been studied in three types of simulated concrete pore solutions. The three types of simulated solutions are NaOH-KOH with pH 11 Ca(OH)2 with pH 12 and NaOH-KOH-Ca(OH)2 with pH 13 respectively. The localized corrosion rates of the carbon steel were measured with coupled multielectrode array sensors (CMAS) when the chloride concentration was changed from 0.0005 to 0.5 mol/L in each solution. Coupons were also used in the tests to verify the results from the CMAS probes. A comparison was made with literature data obtained from other methods.