Self-checkouts (SCOs), also known as assisted checkouts (ACOs) or self-service checkouts, are machines that provide a mechanism for customers to complete their own transaction from a retailer without needing a traditional staffed checkout. When using SCOs, customers scan item barcodes before paying for their total shop without needing one-to-one staff assistance. Self-checkouts are used mainly in supermarkets, although they aren't uncommon in department or convenience stores. Most self-checkout areas are supervised by at least one staff member, often assisting customers process transactions, correcting prices, or otherwise providing service.