The NXT-4X4 Input/Output Expansion Module provides functionality to any Doors.NET™ access control system by adding auxiliary I/O that can be used for additional access control functionality, monitoring non-reader doors or other devices, and creating powerful action sequences by linking input triggers to outputs. The module can be connected anywhere along the RS-485 trunk/buss, most commonly at the controller or near a reader. One module can be added per trunk, allowing up to an extra 8 inputs and 8 outputs on an NXT-2D Controller and an extra 16 inputs and 16 outputs on an NXT-4D Controller.

The module's relays are re-assignable and interchangeable with the main controller's relays. The module can be mounted next to the door providing local door control and local door alarm functions while minimizing the cable bundle from door to controller. The unit also has a port to plug in an NXT-RM3 Reader Interface Module to allow Keri MS reader signals to be sent down the RS-485 line.