20. The method of claim 19 , wherein the initial audio item is a song; and wherein the one or more candidate audio items include different mixes of the song.
19. A method of using a battery powered device to efficiently monitor an audio signal and identify audio items that match the audio signal, the method including: responsive to the battery powered device having sent initial audio fingerprints extracted from the audio signal corresponding to an initial audio item, identifying one or more candidate audio items including fingerprints matching the initial audio fingerprints extracted from the audio signal; updating a first cache from a server with a plurality of audio fingerprint sequences from the one or more candidate audio items and updating the first cache with respective audio item identifiers for the one or more candidate audio items; and matching one or more additional audio fingerprints, extracted from the audio signal after the initial audio fingerprints, to the audio fingerprint sequences of the one or more candidate audio items in the first cache to identify the initial audio item as one of the one or more candidate audio items.