Deal with a security tag the cashier forgot to remove — the safe options, and the one type you should never force.
The fastest, safest fix is returning to the store with your receipt — any location of the same chain has the detacher tool and will remove the tag in seconds. This should always be your first move.
Look at the tag: a hard plastic dome with a pin is a magnetic tag, while one labeled Ink or showing liquid capsules is an ink dye tag. Never pry or force an ink tag — it will burst and permanently ruin the garment.
For pin-style magnetic tags, place a high-strength neodymium magnet directly against the dome side, then wiggle the pin gently until it slides free. Weak fridge magnets won't work; hardware stores sell suitable magnets cheaply.
If the store is far away and the tag is not an ink type, hold the dome steady and wiggle the pin side back and forth with needle-nose pliers, keeping fabric clear so it doesn't tear. Go slowly — snapping the tag risks damaging the clothing.
Check the fabric around the pin hole for pulls or snags and gently smooth the weave closed with your fingers. Keep the receipt in case the item was damaged and needs an exchange.