Mobile devices, such as smartphones, are severely battery-limited. The capabilities of mobile device processors have increased at exponential rates, but battery technologies have improved at much slower rates. As a consequence, it is ever more important that mobile devices be operated in battery-preserving manners. An aspect of the present technology concerns methods and arrangements enabling on-going recognition-processing of imagery and audio by different detectors, without the high battery drain that has characterized the prior art. A variety of other features and arrangements are also detailed.