Nicknamed ''squeakers,'' electronic scanner checkouts at supermarkets are being installed at about 200 stores each month. Offered since 1974, the scanners are electronically ringing up products in 20 percent of US supermarkets, according to the United States Department of Agriculture.
Although opposed in many areas because unit prices are marked only on shelves and not on the goods, the scanners have made gradual headway for several reasons.
One is the absence of mistakes. Consumers shopping in some chain stores are now promised free products for any electronic pricing mistakes. The ''squeaker'' is also said to save stores a fifth to a half penny per sales dollar -- mostly by reducing labor costs for premarking.
The biggest overall benefit comes from analyses of the computer-tallied figures. Individual manufacturers and distributors, where permitted, can plug into a chain's electronic scanner system to determine marketing factors such as a product's rate of sale, purchasing patterns, and the effect of promotional prices.