The Honeywell Home C-Wire Adapter for Wi-Fi Thermostats THP9045A1098 is a white plastic adapter designed to power Wi-Fi thermostats in homes that do not have a C-wire. It is compatible with most types of heating and cooling systems, including furnaces, heat pumps, ductless mini split systems, and through-the-wall/window air conditioners. The adapter is designed for easy adhesive mounting and has a square shape with a 3-inch display for controlling the thermostat. It operates on low voltage and does not require batteries. Perfect for those looking to upgrade their home heating and cooling system to a smart and energy-efficient solution.