18. The system of claim 13 wherein the first stage recognizer classifies the portions of the acoustic input signal based on frequency, order, and distance in time of phrases in the acoustic input signal that match classification keywords.
13. A system comprising: a first stage recognizer operating in an always on mode, the first stage recognizer being configured to: receive an acoustic input signal; classify portions of the acoustic input signal into different classifications using a first speech recognition algorithm, the different classifications corresponding to different topics of interest, each classification being associated with a list of keywords for its corresponding topic of interest; determine, based on the classifying, that a particular topic of interest is being discussed in the acoustic input signal; and trigger, in response to the determining, a second stage recognizer to turn on in order to recognize the acoustic input signal; and a second stage recognizer configured to: recognize, in response to the triggering performed by the first stage recognizer, the acoustic input signal, wherein the second stage recognizer uses a second speech recognition algorithm that is different from the first speech recognition algorithm, and wherein the second stage recognizer recognizes the acoustic input signal based on the particular topic of interest; evaluate one or more potential responses to the recognized acoustic input signal; if at least one response in the one or more potential responses is deemed acceptable, output the at least one response to a user that originated the acoustic input signal; and if no response in the one or more potential responses is deemed acceptable, refrain from outputting anything to the user.