The KT-300 door controller supports up to two readers, which can be installed either on a single door (to monitor both entry and exit) or on two separate doors. It provides connections for all peripheral devices necessary for a complete access control system and can be linked with other door controllers to provide control over millions of doors. Stand-alone mode protects against power or system failures and the system stores cardholder and event data, which is automatically transmitted back to the EntraPass system once the network connection is restored. Flash memory allows for firmware updates from an EntraPass workstation in just a few minutes. Built-in Combus expansion means that relay, input, and output modules can be added to connect HVAC systems, elevators, motion detectors, and more. The Combus is a communication protocol that is integral to the KT-300. It uses a four-conductor cable bus to which several expansion modules can be connected.