This document discusses the value of passive mobile data in understanding consumer behavior. It notes that passive data from smartphones provides important context about consumers' digital environments and activities throughout the day. With smartphones ubiquitous, passive data can reveal when and where consumers are engaging with their devices and apps, which is crucial information for determining when and what types of questions to ask consumers on mobile surveys. The data gives insights into consumers' quick, instinctive behaviors and decisions that they may not be able to consciously recall.