A method and system are provided for adjusting a threshold value of an alarm for a metal detecting system, based on a detected interference with other systems that operate at adjacent frequencies. The method and system include receiving a plurality of sample values and calculating a discrepancy value based on a difference between a maximum value and a minimum value of the plurality of sample values, wherein the discrepancy value corresponds to detected interference. The discrepancy value is compared to a predefined interference threshold value and an activation signal is generated. A fast threshold adjustor receives the activation signal when the discrepancy value is greater than or equal to the predefined interference threshold value and a slow threshold adjustor receives the activation signal when the discrepancy value is less than the predefined interference threshold value. The activation signal triggers an output from the fast threshold adjustor or the slow threshold adjustor that is applied to adjust the threshold value.