The lockbox holds the key to your front door.
An agent has an electronic keypad that will open the box with an infra red beam after entering their identifying security code.
The box does not register who came into your home. The keypad in the agent's hand, when updated, is what records which homes that agent went into today.
The agent cannot go out the next day, or the next time they need to show homes, without updating that keypad. So while the registration of who was in your home is not immediate. And active agent will update their pad more often than an inactive agent.
Usually we can print out a list every day of everyone who was in the home.