HEATS exposure: protocol for wearable and in-home monitoring of indoor environment, sleep, and activity in Singapore
Abstract: Heat exposure increasingly threatens health in tropical urban settings, where elevated temperatures persist day and night. Sleep and physical activity are critical outcomes, yet evidence often relies on outdoor metrics that may not reflect indoor exposures. Indoor bedroom conditions, near-body thermal exposure, and adaptations like air-conditioning or fan use are likely more relevant to sleep-related heat burden but remain underexamined in free-living populations. This protocol describes a longitudinal field study investigating the interactions between real-world heat, bedroom environments, sleep, and physical activity among working-age adults in Singapore. The study aims to recruit up to 150 healthy adults, monitored under free-living conditions in their usual home environments for approximately 60 days per individual. Data integration includes smartwatch-based ecological momentary assessments, wearable physiological and activity monitoring, continuous bedroom environmental sensing, and near-body temperature measurement. Primary sleep outcomes are total sleep time (TST) and wake after sleep onset (WASO). Secondary outcomes include daily physical activity, cardiovascular measures, and repeated self-reports on thermal perception, sleep disruption, and adaptive behaviours (e.g., cooling system settings). Monitored bedroom variables include air temperature, relative humidity, sound pressure, CO₂, formaldehyde, particulate matter (PM₁, PM₂.₅, PM₁₀), TVOC index, atmospheric pressure, and illuminance. Linear mixed-effects models will examine within-person associations between environmental exposures and sleep, with further analyses planned for physical activity, near-body versus ambient exposure comparisons, and non-linear relationships. This protocol provides an operationally scalable framework for studying residential heat-health relationships. By combining room-level, near-body, wearable, and self-reported data, the study will identify environmental metrics most relevant to sleep and activity and how behavioural adaptations shape these relationships. Findings may inform future heat-health guidance, indoor cooling and ventilation strategies, and interventions to reduce heat-related sleep disruption and support thermal resilience in tropical urban populations.
Full text available at: BMC Public Health
Recommended citation: Renard, M., Frei, M., Chua, Y. X., Zhang, W., Parkinson, T., Lo, J. C.-Y., Lee, J. K. W., Schiavon, S., & Miller, C. (2026). HEATS exposure: protocol for wearable and in-home monitoring of indoor environment, sleep, and activity in Singapore. BMC Public Health. doi:10.1186/s12889-026-29597-y