An anti-theft magnetic strip is a security feature used in retail stores to prevent shoplifting.  The strip is attached to the merchandise and contains a magnet that sets off an alarm if it passes through a detection system at the store’s exit without being properly deactivated.  The strip helps deter theft by making it difficult for shoplifters to remove merchandise without triggering the alarm.  It is often used in conjunction with other security measures, such as surveillance cameras and security personnel.