Nest Labs isn't counting solely on the allure of discounts from power companies to reel us in this spring. It's pushing out a 3.5 update to all versions of the Nest Learning Thermostat that should be make it smarter about saving money -- even if it means spending a little up front. Along with the utility tie-ins from last week, the upgrade adds a Cool to Dry mode that invokes air conditioning when it's too humid, raising the energy bill slightly to avoid a costlier mold outbreak. The thermostat also won't be easily duped by the sun: a new Sunblock setting prevents unnecessary cooling whenever direct sunlight affects the temperature reading. Homeowners who just want more precision, meanwhile, may be happy with both refined fan scheduling (shown above) as well as mobile app updates that introduce alert messages and a more thermostat-like interface. Those with Nest units connected to WiFi should see version 3.5, and hopefully its intended savings, by 9PM Eastern tonight.