A swing tag is an informational text attached to a garment for sale and can be also known as a swing ticket. Unlike a laundry symbol or size marker that are sewn into a garment, swing tags are not part of a garment: a swing tag may be attached to the garment by thread or by a plastic joiner.
Swing tag Wikipedia
Swing tags are used on items that are sold in a store usually worth a high value. They are activated by a magnetic lock system which can only be triggered by passing through a security gate which will most likely be at the entrance/exit of the store. Once activated an alarm will sound alerting staff that someone is trying to shoplift. They are a simple security device that is used all throughout the worlds stores, commonly in clothing brands. The only way to remove them is with a magnetic machine at the counter of the shop where a pin is forced upwards to detach the tag from the item. However people have been known to try and force these off. This is not a wise idea as almost every swing tag will contain a solution of acid that can cause irritation or corrosion to the skin, the acids used in these tags can vary, common acids include hydrochloric acid, sulfuric acid, nitric acid, chromic acid, acetic acid and hydrofluoric acid, common bases are ammonium hydroxide, potassium hydroxide (caustic potash) and sodium hydroxide (caustic soda). The swing tag will burst on a forced attempt to remove and spray acid on the skin.