Why a duty-free bag gets sealed
A bottle bought after airport security may still have to pass through another checkpoint during a connection. That can be a problem for liquids: screening rules may limit the size of containers passengers can carry through, even when the liquid was purchased at an airport shop.
A tamper-evident bag helps bridge that gap. The shop places the purchase inside and closes the bag with a seal designed to show visible damage if someone opens it. The receipt is often kept with the purchase so screeners can check what was bought and where.
What the seal tells screeners
At a transfer checkpoint, staff can inspect the sealed package instead of treating it like an ordinary, opened container. An intact seal provides a quick visual sign that the bag has not been accessed since the purchase; if it is broken, the contents may need additional screening or may not be allowed through.
The seal is not a security test of the liquid itself. It preserves a visible chain between the shop and the checkpoint, making a bag that has remained closed easier to assess. That is why opening it during a layover can turn a straightforward transfer into a screening problem.
