Wal-Mart plans to roll out sophisticated electronic ID tags to track individual pairs of jeans and underwear, the first step in a system that advocates say better controls inventory but some critics say raises privacy concerns.

While the tags can be removed from clothing and packages, they can't be turned off, and they are trackable. Some privacy advocates hypothesize that unscrupulous marketers or criminals will be able to drive by consumers' homes and scan their garbage to discover what they have recently bought.

They also worry that retailers will be able to scan customers who carry new types of personal ID cards as they walk through a store, without their knowledge. Several states, including Washington and New York, have begun issuing enhanced driver's licenses that contain radio- frequency tags with unique ID numbers, to make border crossings easier for frequent travelers. Some privacy advocates contend that retailers could theoretically scan people with such licenses as they make purchases, combine the info with their credit card data, and then know the person's identity the next time they stepped into the store.