VDI interface can monitor up to 64 (4x16) opto-isolated DC voltage inputs or up to 64 dry contact inputs or a combination of both. Each input can be programmed to perform a variety of alert monitoring tasks. It can monitor Voltage present and Voltage absent. In addition it will recognize 1Hz and 2Hz pulsing inputs. The unit was designed to operate with the Scope ConneXions series paging transmitter.