Abstract
This article reviews the Electronically Activated Recorder or EAR as an ambulatory ecological momentary assessment tool for the real-world observation of daily behavior. Technically, the EAR is an audio recorder that intermittently records snippets of ambient sounds while participants go about their lives. Conceptually, it is a naturalistic observation method that yields an acoustic log of a person's day as it unfolds. The power of the EAR lies in unobtrusively collecting authentic real-life observational data. In preserving a high degree of naturalism at the level of the raw recordings, it resembles ethnographic methods; through its sampling and coding, it enables larger empirical studies. The article provides an overview of the EAR method, reviews its validity, utility, and limitations, and discusses it in the context of current developments in ambulatory assessment, specifically the emerging field of mobile sensing.