The Nationwide Siren Warning System of the Republic of Bulgaria allows the integration of third-party siren warning systems to it via the B2B interface for migration of third party sirens. 

For the control and supervision of those sirens, a universal Third Party Siren RTU (SEWA-RTU) has to be used.

The NSEWA-RTU is the gateway between the Nationwide system network and the siren. The third-party siren must be of electronic type (no mechanic sirens etc.)

The control and supervision are handled by the Hörmann Open Interface (HOI) protocol or alternatively MODBUS-RTU.

If you are the owner or installer of such a system, please consult the information below and contact us for more information.

Rules and guidelines for integration of third-party sirens

  • for migration of a third-party siren, there have to be installed an NSEWA-RTU at a site connected to the third party siren
  • for functional impact security as well as general network security it is not possible to connect any equipment directly to one or more of the SEWA communication channels and media.

basic technical requirements for the sirens:

  • the third party siren must fulfill all requirements and functionality of the Nationwide Siren Warning System 
  • must fulfill all requirements especially in terms of protocol handling, status value mapping and necessary measurement equipment and routines in the siren
  • must be µ-Processor-based architecture able to communicate with the NSRPO-RTU
  • must have built-in test routines supervising basic siren conditions permanently (24/7) without external trigger as there are at least mains supply, cabinet door, battery idle voltage, battery symmetry 
  • must report failures on supervised equipment automatically by sending unsolicited alarms 
  • must be able to perform full-scale self-test including load tests (e.g. batteries, amplifiers, drivers), the storage of the results and report 
  • must contain automatic self-supervision of software and hardware modules to re-establish a link to SEWA-RTU in case of failure or lock

Technical Approval and Certification


  • Any third party siren hardware and software interface must be approved by Hörmann whereby the manufacturer stays responsible for the third-party siren's function itself.
  • this can be done by sending a siren sample model to Hörmann for approval of the control protocol
  • It is preferable to perform the test within an IFAT procedure (Integrated Factory Acceptance Test) at Hörmann premises together with the third party siren manufacturer.
  • It is third party siren manufacturers responsibility in time and costs to supply test equipment accordingly
  • After successful test Hörmann supplies a certificate for the tested software and hardware interface.
  • It is third party siren manufacturers responsibility to ensure the provision of same certified software and hardware as for final installation and operation