To understand the potential exposure to tobacco smoke in Washoe County (Reno/Sparks), Nevada casinos by measuring air quality in smoking areas relative to non-smokingon-gaming areas in which minors may be present. To act as a pilot study in community-based health research and policy campaigns by evaluating low-cost air monitors to measure personal secondhand smoke (SHS) exposure. We used customized mobile apps, AtmoTube PRO Air Monitors, and hand clickers to measure the timing and minute-by-minute levels of PM2.5 (a tobacco smoke marker). The app was used to record the number of smokers, minors, and total patrons associated with ~10-minute sequential time periods in standardized casino locations, including outdoor areas, slots, tables, restaurants, bars/lounges, arcades, among others. Between April and May 2022, we successfully visited 14 casinos and 18 distinct types of indoor casino locations. We found high PM2.5 peaks in casino locations even with zero, or a low percentage of, observed active smokers, including in both gamingon-gaming areas. Indoor areas, regardless of smokingon-smoking areas, consistently had higher PM2.5 levels than outdoor background levels. Indoor locations had median PM2.5 levels up to 18 times higher than the lowest outdoor background levels. Minors were present throughout all casino locations, and thus were likely exposed to elevated PM2.5 levels. Potential PM2.5 exposures due to smoking can be high regardless of ventilation systems. Small proportions of smokers in a location can lead to high levels of exposure. Establishing comprehensive smoke-free casinos is the only way to protect against SHS harms.