Sleep mode gradually adjusts the temperature throughout the night to match the body’s natural cooling cycle. This energy-saving feature is found in the MRCOOL Olympus 4th Gen Wall AH 18,000 BTU. It prevents the room from getting too cold or too hot while you sleep. Many of our Wall Mounts 2 Zones products emphasize this for bedroom installations. It also reduces fan noise to its lowest setting for a peaceful environment. This mode is a smart way to lower your utility bills.