What does "Listed central station" mean?

"Listed central station" is a common way to refer to an alarm monitoring facility that has demonstrated the ability to provide Standards complying service. In the case of monitoring stations, UL requirements cover building structure, receiving and monitoring equipment, and staffing issues; in addition to installation and ongoing service. In order to be able to provide Standards complying service, the building, equipment and staffing requirements have to be met at all times. However, the handling of specific signals form specific alarm systems is only audited by UL if a Certificate is in effect for that alarm system.