Hugh Silcox of Baltimore installed a wireless thermometer in the concrete back "yard" of his rowhouse. Last Saturday it read 110 degrees. "Clearly the thermometer was basking in a direct beam of sunlight," he said. "Should I place the thermometer under an upturned flowerpot? Seems too cool to me." Keep looking, Hugh. Your yard's a solar furnace. Shade the sensor from direct sun and mount it away from brick or concrete, which absorbs and re-emits solar heat. It also needs air circulation. Five feet above grass is ideal.