Smart thermostats have been dropping in price steadily as more players enter the market, so there's really no reason to install a dumb model these days. But if you're working with a tight budget, and don't mind giving up some of the fancier features the top-shelf models offer, this one from iDevices works with all three of the major digital assistants--Alexa, Google Assistant, and Siri--and it can be integrated into Apple's HomeKit ecosystem, too. It's not the slickest or most feature-rich thermostat you'll find, and doesn't offer the highest build quality--heck, it doesn't even have a trademarked name--but you can pick one up on Amazon for about $100. Outfitted with a tiny, 2-inch, color LED display inside a glossy white enclosure, iDevices assumes you'll manage it with either voice commands via a smart speaker or with its mobile app. It can control one- and two-stage heating, heat pump, and cooling systems; and ventilation fans.