Residents across a large neighborhood notice that official weather reports do not capture differences between shaded streets, open parking areas, and homes near the river. A local college helps them install a small network of temperature and rainfall sensors. Choosing locations requires care. A sensor beside a dark wall may record reflected heat, while one beneath a tree may miss part of a storm. Volunteers follow shared placement rules, photograph each site, and record when buildings or vegetation change. The devices send compact readings through a low-power radio network to a public dashboard. Software checks for missing values, impossible jumps, and sensors that remain unchanged for too long. Suspect readings are marked rather than silently deleted. During the first heat wave, the map shows that blocks with mature trees cool earlier in the evening than wide paved areas. The result supports further study, but the group avoids claiming that trees are the only cause. Wind, building height, and sensor placement also matter. Students compare observations with a calibrated station and adjust instruments when a consistent bias appears. Community members can download the data and read plain explanations of its limits. The network becomes useful because its measurements are transparent and repeatable. Inexpensive technology does not remove the need for careful method; it makes careful observation possible in more places.