The lock mechanism on a regular door works simply: A metal piece moves in and out of a hole or notch in the door frame when someone turns the handle. When you've locked the handle, the metal piece doesn't move, and the door won't open. But all you have to do is make the metal move out of the way and the door will open easily. This can be done by inserting a credit card between the metal and the door frame. You can prevent credit card entry in several ways.
Educate yourself on how a lock can be bypassed with a credit card. By understanding how it works, you can take steps to prevent it in the future. See the Resources section for a short video demonstrating how a credit card can be used to open your lock.
Install a door latch guard. This metal plate follows the contour of the door frame, extending over it. It is designed to prevent someone from sliding a credit card into the space between the door and the frame.
Use a dead bolt on your door. A dead bolt is a much longer piece of metal—or bolt—that is inserted far into the door frame, whereas a door handle lock only uses the small piece of metal that can be moved with a credit card. Install additional dead bolts on your door for extra security.
Add a sliding door latch to your door. Similar to a dead bolt, a sliding door latch, with its long metal bar, cannot be moved out of the way by a credit card.
Install an electronic door handle on your outside doors. These locks have keypads that require a code to be punched in to gain entry. There is not a space to slide a credit card into these locks.