7. The processor-implemented method of claim 6 , further comprising: producing a first score indicating a first likelihood that the trigger expression is represented by the first audio signal; comparing the first score to the first threshold; producing a second score indicating a second likelihood that the trigger expression is represented by the second audio signal; and comparing the second score to the second threshold.
7. The processor-implemented method of claim 6 , further comprising: producing a first score indicating a first likelihood that the trigger expression is represented by the first audio signal; comparing the first score to the first threshold; producing a second score indicating a second likelihood that the trigger expression is represented by the second audio signal; and comparing the second score to the second threshold. 8. The processor-implemented method of claim 7 , wherein producing the first score comprises: creating an acoustic model of the utterance represented by the first audio signal; and comparing the acoustic model to one or more reference acoustic models that correspond to the trigger expression.