Del. Code tit. 4, § 720

All holders of licenses for the sale of alcoholic liquor in a tavern, restaurant or taproom, and as to the public sale portions of the premises covered by holders of a hotel or club license, shall store all alcoholic liquor in adequate storage facilities and the premises, or the part of the premises where such alcoholic liquor is stored if a hotel or club, must be locked before the last person leaves the licensed premises.