Honeywell YTH5320R1000 Wireless Focuspro Thermostat Kit, Non-Programmable Redlink Enabled EQUIPMENT INTERFACE MODULE(EIM): All HVAC equipment is wired to the module. Module receives communication from the wireless devices RETURN AIR SENSOR: Works with the Equipment Interface Module to maintain safe indoor temperatures if power is lost at the wireless thermostat. Maintains 62 F for heating and 82 F for cooling