Traditional smoky cooking fires are one of today's greatest environmental threats to human life. These fires, used by 40% of the global population, cause 3.9 million annual premature deaths. "Clean cookstoves" have potential to improve this situation; however, most cookstove programs do not employ objective measurement of adoption to inform design, marketing, subsidies, finance, or dissemination practices. Lack of data prevents insights and may contribute to consistently low adoption rates. In this study, we used sensors and surveys to measure objective versus self-reported adoption of freely-distributed cookstoves in an internally displaced persons camp in Darfur, Sudan. Our data insights demonstrate how to effectively measure and promote adoption, especially in a humanitarian crisis. With sensors, we measured that 71% of participants were cookstove "users" compared to 95% of respondents reporting the improved cookstove was their "primary cookstove." No line of survey questioning, whether direct or indirect, predicted sensor-measured usage. For participants who rarely or never used their cookstoves after initial dissemination ("non-users"), we found significant increases in adoption after a simple followup survey (p = 0.001). The followup converted 83% of prior "non-users" to "users" with average daily adoption of 1.7 cooking hours over 2.2 meals. This increased adoption, which we posit resulted from cookstove familiarization and social conformity, was sustained for a 2-week observation period post intervention.