How to Tell if Someone Opened Your Door

How to Tell if Someone Opened Your Door

Which of These Items Can Help You Tell if Someone Opened Your Door?

  • Key
  • Hair
  • Door Knob
  • TEST
  • Penny

Answer: Hair or Penny

If you answered “hair” or “penny,” either you took a lucky guess or you already know one of these tricks. You shouldn’t have to worry about someone violating your privacy by going through a door they shouldn’t, but assuming security can be dangerous. Sometimes the most charismatic people are really the most dangerous and sly ones.

Secure the Door with a Hair

A hair, string, or anything very small and hard to see works well for this trick. First, put a light notch in the door or doorframe, using a needle or something else that can leave only a small mark. You might even just make a light line with a pencil.


Next, place the hair between the door and the door frame. You can also place it on top of the door — just as long as you know exactly where it is. When someone opens the door, the hair will fall. When you return to check, simply look at the place where the hair should be before you open the door. If it’s still there, no one opened it. The mark serves as a secondary security measure in case someone saw the hair before they opened the door and replaced it before closing the door again.

Buy Security for a Penny

You can do the same thing with a penny as you did with the hair, but you also risk the penny attracting attention when it falls. Try a different method to avoid that risk.

Place a penny on the floor, fairly close to the door inside your room or house. When you shut the door, slide a piece of paper under it. It works even better if you can lean the paper against the door, or place it on top of the door. When the door opens, the paper will move, covering the penny. This is an especially effective method if you happen to be a bit of a messy person, because it won’t stand out to anyone entering the room or house.


It’s also a good idea to take pictures of rooms before you leave, if you have security concerns. When you return, you can compare the images with the current state of things, paying close attention to areas around drawers, closets, and other places where you might try to secure your belongings.