LAUSR

&NA; Exposure to household air pollution is a leading cause of morbidity and mortality globally. However, due to the lack of validated low‐cost monitors with long‐lasting batteries in indoor environments, most epidemiologic studies use self‐reported data or short‐term household air pollution assessments as proxies of long‐term exposure. We evaluated the performance of three low‐cost monitors measuring fine particulate matter (PM2.5) and carbon monoxide (CO) in a wood‐combustion experiment conducted in one household of Spain for 5 days (including the co‐location of 2 units of HAPEX and 3 units of TZOA‐R for PM2.5 and 3 units of EL‐USB‐CO for CO; a total of 40 unit‐days). We used Spearman correlation (&rgr;) and Concordance Correlation Coefficient (CCC) to assess accuracy of low‐cost monitors versus equivalent research‐grade devices. We also conducted a field study in India for 1 week (including HAPEX in 3 households and EL‐USB‐CO in 4 households; a total of 49 unit‐days). Correlation and agreement at 5‐min were moderate‐high for one unit of HAPEX (&rgr; = 0.73 / CCC = 0.59), for one unit of TZOA‐R (&rgr; = 0.89 / CCC = 0.62) and for three units of EL‐USB‐CO (&rgr; = 0.82–0.89 / CCC = 0.66–0.91) in Spain, although the failure or malfunction rate among low‐cost units was high in both settings (60% of unit‐days in Spain and 43% in India). Low‐cost monitors tested here are not yet ready to replace more established exposure assessment methods in long‐term household air pollution epidemiologic studies. More field validation is needed to assess evolving sensors and monitors with application to health studies. HighlightsWe assessed PM2.5 and CO low‐cost monitors in semi‐controlled and field studies.Devices experienced high failure rate and susceptibility to environmental changes.Low‐cost monitors tested may not be ready to replace more established methods.