No, unscanned barcodes don't set off alarms. In contrast, all barcodes do not trigger an alarm. What triggers the alarm is the magnet. However, magnets are usually placed near the barcode so the cashier knows and can deactivate the magnet simply by scanning the item. That makes many people mistakenly think that unscanned barcodes set off alarms. Usually, magnets are found in products with high theft or expensive products. For example, a $5 item might also have a magnet if it's susceptible to theft. It can also be on shopping carts or streetcars because retailers don't want their assets to leave the building.