Abstract: An electronic lockbox with a single sensor that can detect both the position of a key compartment component (or a movable key bin) and the presence of a removable key fob (attached to a building key). The key compartment includes a first magnet and the removable key fob includes a second magnet. The single sensor can detect the presence of neither magnet, the first magnet alone, or both the first and second magnet together. If neither magnet is detected, then the key compartment (movable bin) is open. If only the first magnet is detected, then the key compartment (movable bin) has been closed without the removable key fob. If both the first and second magnets are detected, then the key compartment (movable bin) is closed with the removable key fob inside the movable bin.