Most retail stores, as you know, have security tower devices which detect when items with tags pass through the front door, sounding an alarm.
Shoplifters turn to what is called a booster bag: in this case, a regular shopping bag lined with aluminum foil. This is also known as a Faraday cage. It shields the tags from begin detected by security.
In case you are guessing, yes, this is illegal. In the case of Francesca Cenatis vs. State of Florida, she was spotted (the good old fashion way: by employees) allegedly trying to steal items using a battered Victoria’s Secret bag lined with foil. It appears the booster functioned as intended — just that she was apprehended by employees who saw her. And she was arrested anyways. Use of such a bag is illegal, according to the Fourth District, under F.S. 812.015, Florida’s Antishoplifting Device Countermeasure Statute.
Before we receive gripes and emails about aiding or encouraging someone to break the law: folks, if the instructions are (widely available) on the internet, it is (a) unlikely that this law-related site is going to lead you into a life of crime and (b) it is also likely well-known to shop owners, who have
beaten you to the punch and trained employees and have employed better security measures before this “bright” idea came to you.