Most smart thermostats require a blue "C" wire to provide constant power.
Upgrading your thermostat is one of the most effective ways to lower energy bills and improve home comfort. Quick Summary: Which One Should You Buy? buy thermostat
Amazon Smart Thermostat (simple, works great with Alexa). Most smart thermostats require a blue "C" wire
Google Nest Learning Thermostat (sleek design, learns your schedule automatically). learns your schedule automatically).