What is foil around door knobs when alone?

Foil around door knobs is a common trick used to detect whether someone has entered a room or not. The idea is that if someone turns the door knob, they will crinkle or move the foil, indicating that someone has been in the room. This can be used as a safety measure, especially when you are alone and want to ensure that no one has entered your room without your knowledge. Additionally, it can be used as a way to determine if someone is snooping around in your belongings, as you will be able to tell if the foil has been disturbed. However, it is not foolproof and should not be relied on as the only safety measure. It is important to also ensure that doors are locked and secure, and to take other precautions to prevent unauthorized entry.