1. A method for spotting words in a speech signal, the method comprising the steps of: generating a first recognition score based on the speech signal and a lexicon entry for a first word, the first recognition score tracking an absolute likelihood that the first word is in the speech signal; estimating a first background score based on the first recognition score; and calculating a first confidence score based on a matching ratio between a first minimum recognition value and the first background score, the first confidence score tracking a noise-corrected likelihood that the first word is in the speech signal.