10. The system of claim 8 , wherein determining that a shape of at least a portion of the audio input signal matches a shape of at least a portion of an audio trigger signal corresponding to a keyword comprises: determining a relationship, between one or more maxima in the portion of the audio input signal and one or more minima in the portion of the audio input signal, satisfy more than one condition.
10. The system of claim 8 , wherein determining that a shape of at least a portion of the audio input signal matches a shape of at least a portion of an audio trigger signal corresponding to a keyword comprises: determining a relationship, between one or more maxima in the portion of the audio input signal and one or more minima in the portion of the audio input signal, satisfy more than one condition. 11. The system of claim 10 , wherein determining a relationship, between one or more maxima in the portion of the audio input signal and one or more minima in the portion of the audio input signal, satisfy more than one condition comprises: determining at least that a ratio between a maxima and a minima satisfy a threshold.