Lock boxes provide a means for real estate agents and their clients to access a listed property. They look like a regular padlock, with a ring large enough to be hung around a doorknob or handle. An entry key inside the box is accessed via a combination code.
Combination codes are usually kept on file at the listing agent's office, and buying agents can simply call and provide their clearance information to get the code. All the agents have to do is punch in the code to retrieve the key. High-quality lock boxes are secure enough to prevent anyone with illicit motives from accessing the key.