AutoVac keeps wine fresher, longer – automatically! It pumps air out and seals flavor in, so you can enjoy a bottle over several days. Just place on bottle, automatic operation instantly seals your bottle of wine and removes air. Simply leave the wine preserver in place. The AutoVac keeps working automatically, senses if any air is seeping back into the bottle and activates as needed. Auto shut-off. Uses 2 AAA batteries (not included).