What is aluminum foil on door knobs when home alone?

It has been suggested by some security experts that wrapping aluminum foil around the door knob when home alone can serve as a deterrent to potential intruders. The idea is that the foil would create an audible noise or electrical shock if someone attempts to twist or open the door, alerting the occupant and potentially scaring off the intruder. It is worth noting, however, that this method is not foolproof and should not be relied upon as the sole method of home security. It is important to also have strong locks, secure windows, and a reliable alarm system.