1. A method for identifying a speaker in an energy-efficient manner, comprising: at a first processing unit: determining whether a received audio signal satisfies an audio strength test; and if the audio strength test is satisfied, determining whether the audio signal contains human speech; and at a second processing unit: identifying whether speech frames, obtained from the audio signal, have a quality which satisfies an admission test, the speech frames which satisfy the admission test comprising admitted frames; and associating a speaker model with the admitted frames, the speaker model corresponding to a particular user, operations performed by the first processing unit having a first power expenditure and operations performed by the second processing unit having a second power expenditure, the first power expenditure being less than the second power expenditure.