A booster bag is a bag which has been designed to conceal stolen merchandise. There are a number of creative variations on this bag, all of which are designed to make thieves difficult to identify and track, and in many stores, patrons are required to check their bags at the counter to avoid the use of booster bags.
Originally, the term was used simply to refer to an especially large bag used to stow away stolen merchandise, and sometimes to garments outfitted to assist thieves. In the modern era, the booster bag has gotten more high-tech: thieves line bags with aluminum foil so that signals from anti-theft devices are blocked, allowing the thief to walk through anti-theft detectors without fear. In addition to lining large bags with foil, thieves can also line clothing to turn themselves into walking booster bags.
The advantage of a foil-lined booster bag for thieves is that it can look perfectly ordinary, allowing the thief to browse the store like any other customer. Because the bag blocks signals from tags, the thief doesn't have to attempt to remove or alter the tags, and since store security are on the lookout for suspicious behavior like long trips to the fitting room, thieves fall below the radar. Thieves also don't need to be nervous when walking out the door, as they can be confident that the signals from the tags in the garments or stolen objects will be blocked.
For stores, of course, foil-lined booster bags pose an immense problem. While stores can ask clients to check bags at the counter, it is not uncommon for women to hold on to small purses and satchels, and in a store with small, expensive items, such a purse can easily be used to conceal stolen items. In stores without counter checks, security have to be especially alert for signs of theft if they want to catch someone in the act of using a booster bag.
In another creative variation on the classic booster bag, a thief cuts a hole in the bottom of a large shoulder bag, allowing the thief to position the bag over someone's purse or bag while it is sitting on a bench or table. The thief can grasp the purse through the hole, allowing him or her to carry the bag off and inspect it at leisure. Especially in crowded areas, it can take the victim some time to realize that the bag has been snatched, and it can be a challenge to identify the thief, since holding a large shoulder bag is an ordinary activity which normally would not attract notice.