Certain aspects involve an interface device for a distributed antenna system (“DAS”). In some aspects, the interface device can include an interface, a power detector, and a processor. The interface can include one or more ports for communicatively coupling the interface device to a base station and a switch that is switchable between first and second configurations. The first configuration connects a port to a downlink path of the DAS, and the second configuration connects the port to a signal reflection path. The processor can switch the switch between the first and second configurations based on a signal power measured by the power detector at the port. In other aspects, the interface device can include additional ports and termination loads. The processor can cause a signal path to be connected to a termination load instead of a port based on the port being disconnected from a unit of the DAS.