Honeywell YTL9160AR1000 E-Connect Wireless Programmable/Non-Programmable Line Volt Thermostat Kit 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 Red link wireless technology: powered by red link reliability. No interference with other wireless devices in the home