Self-checkout (also known as Self-service checkout, or a Semi Attended Customer Activated Terminal (SACAT)) machines provide a mechanism for customers to pay for purchases from a retailer without direct input to the process by the retailer's staff. They are an alternative to the traditional cashier-staffed checkout.
As of the end of 2008, there were 92,600 self-checkout units worldwide. The number is estimated to reach 430,000 units by 2014.
In self-checkout systems, the customer is permitted to scan the barcodes on their own items, and manually identify items such as fruits and vegetables (usually with a touchscreen display), which are then weighed where applicable, and place the items into a bagging area. The weight observed in the bagging area is verified against previously stored information to ensure that the correct item is bagged, allowing the customer to proceed only if the observed and expected weights match.
Payment on self-checkout machines can be accepted by various methods: card via EFTPOS, debit/credit cards, electronic food assistance cards, cash via coin slot and bank note scanner, and in-store gift cards where applicable. Most coupons also have barcodes and can be scanned the same way that items are scanned although some require attendant entry.
The benefit to the retailer in providing self-checkout machines is in reduced staffing requirements since one attendant is all that is required to run four to six checkout lanes at one time, which can also reduce checkout time for customers.
Self-checkout is vulnerable to some shoplifting techniques. However, in many cases the machine will pick up the attempt to steal or else cause the shopper to alter behavior (e.g., put an item not on the scales but somewhere else where it should not be put and will be noticed by the system supervisor). For example, in 2007, a man was charged with replacing the tag of a plasma TV with a $4.88 DVD, and trying to purchase it through self-checkout.
An alternative system consists of a portable barcode scanner that is used by the customer to scan and bag items while shopping. When the customer has finished shopping, the scanner is brought to a checkout kiosk, where the information from the barcode scanner is downloaded to the kiosk, usually in conjunction with a customer loyalty card. The customer pays and receives a receipt at the checkout kiosk. The integrity of the system is maintained through the use of random audits or RFID.
Suppliers like NCR, Wincor-Nixdorf and others have manufactured hybrid checkout systems that allows the checkout counter to be switched between either a cashier operated mode or a customer self-service mode. 
HybridCheckout from PeoplePos has taken the hybrid concept further by allowing the cashier and customer to do parallel and simultaneous scanning. This is achieved by adding a customer scanning area next to the cashier scanning area. The HybridCheckout solution allows for an increased throughput and a combination of cashier operated scanning and customer self-service.
BBC News reported in December 2009 on the rise of self-service tills and how error messages like 'unexpected item in the bagging area' are becoming part of the new shopping experience and even given rise to t-shirts bearing the slogan.
Another increasingly vocal critique of the self-checkout system is that it robs the retailers of another opportunity to interact with their customers.
An appeal court in California confirmed in September 2013 a bill banning sales of alcoholic beverages in self-service checkouts. The law requires alcohol only to be sold in face-to-face transactions with store clerks.
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- Daniella Miletic (April 22, 2008). "A new way to shop — check it out for yourself". Melbourne: The Age. Retrieved 2008-09-02.
- Guy Switches Price Tag On Walmart Plasma TV, Tries To Buy It For $4.88
- Self-Check Kiosk from Scratch: Iowa Librarian's Coding Skills Prove Valuable
- Oxford Developments at GAUG 2002 Archived from the original on 24 November 2012
- Ceridwen Open Source Self Issue Client
- Winterman, Denise (2009-12-09). "The problem with self-service checkouts". BBC News. Retrieved 9 June 2013.
- Anand, Anika (07/10/2011). "Major grocer getting rid of self-checkout lanes". NBC News. Retrieved 9 June 2013.
- Cunningham, Tessa (2011-04-07). "Unexpected item in the bagging area: a human!". London: dailymail.co.uk. Retrieved 2011-04-12.