What is tin foil on door knob when alone?

Placing tin foil on a doorknob when alone is often believed to act as a way to detect if someone has entered a room or a house uninvited. The idea behind this method is that when someone touches the doorknob in an attempt to enter, the tin foil will wrinkle or crinkle, alerting the person who placed it. However, there is no guarantee that this method is effective or foolproof. Additionally, it is important to note that such DIY security measures are not a substitute for professional security systems and precautions.