What is foil on door knob when home alone?

The idea behind putting foil over a door knob when home alone is to prevent someone from entering the room undetected. It creates a crinkling noise when someone tries to turn the knob, which can alert the homeowner or make the intruder think they’ve been caught. However, this method may not be foolproof and should not be relied upon as the only means of protection. There are other safety measures, such as locking doors and windows, installing a security system, and having a plan in case of an emergency, that should also be implemented when home alone.