This paper introduces the design of a low-power and low-cost audio recorder. Although the initial purpose is the study of wildlife behavior, the result can be applied to many other fields including urban noise cartography or industrial monitoring. The system is based on a minimal set of low-cost, off-the-shelf components (MEMS microphone, microcontroller, and SD card). Focus is given to autonomy both in terms of embedded energy and data storage. The paper demonstrates that both are improved by applying an online embedded compression to the audio data. Together with an ingenious use of available hardware resources, we were able to lower the overall power consumption compared to existing solutions by an order of magnitude, at equivalent audio quality.