The Model 391 Dante® Alerting Unit builds on the limited capabilities of the "beacon" or "strobe" devices that are ubiquitous with analog party-line (PL) intercom systems and adds a broad range of new and enhanced features. The Model 391 responds to audio "call" signals that are present in the unit's Dante audio input channels. With an 18-23 kHz detection range, it will detect tone call signals that are commonly utilized in both legacy analog and modern digital PL intercom circuits.