Most smart thermostats require a Wi-Fi connection to function properly, as they rely on internet connectivity to communicate with their companion apps and other smart home devices. Without Wi-Fi, you may not be able to remotely control the thermostat or access its full range of features. However, some smart thermostats may offer limited functionality without Wi-Fi, such as basic temperature adjustments using the thermostat's touchscreen interface. It's important to check the manufacturer's specifications and requirements before purchasing a smart thermostat, to ensure that it will work with your home's Wi-Fi network and meet your needs.