Acoustic warning systems have been used to provide warnings in emergency situations for ages. Beating on various metal objects was used in ancient times; later bell towers were built for this purpose and at the beginning of the 20^th century mechanical rotating sirens started to appear. These are basically formed by an electric motor with a specially treated head that emits a sound while rotating. Even now these sirens are used in many countries. The development of electronics, however, has also influenced this area and first electronic sirens started to appear at the end of the 20^th century. Electronic sirens are basically high-performance sound signal electronic amplifiers just like those in home sound systems. However, these sirens work with substantially higher outputs and specific demands are placed on them in terms of desired extreme reliability and different methods of their control. Control infrastructure must also be reliable and usually two independent control channels are required. The loudspeakers for these amplifiers are placed in specially-designed sound baffles and they play the signals stored in the siren’s digital memory or signals fed to the siren from external sources – a microphone, phone, radio station, common radio and television broadcasting, etc. Telegrafia currently offers two product lines of state of the art electronic sirens: PAVIAN and GIBON.

Siren applications and to a large extent siren technical requirements are defined directly by law in many countries. Even though the requirements in question are similar, from the technical point of view they are so different that they cannot be met by a single version of a siren alone. Not only are the requirements related to acoustic announcements different but also those related to control methods and siren status control. Great attention is also paid to siren backup in the case of a power failure. That is the reason why a modern siren, i.e. a modular device with many firmware versions from the hardware point of view, is normally backed up by batteries and designed in such a way that electric power supply is used at a minimum when it is not active and the conversion of electric power into acoustic power is at peak efficiency when the siren is active.

Sirens are either used as separate, locally controlled equipment or as a part of warning systems, which is their most common application. Unlike the small systems consisting of several sirens, large systems can be formed by thousands of sirens. Considering the fact that these systems are used only in the situations of real danger, which is an occasional event, one has to be sure that they will really function at the time when they are actually needed. Therefore great demands are placed on automatic testing functions in connection with both sirens and related infrastructure. Experience from all over the world shows that power failures and telecommunication infrastructure failures virtually always occur during emergencies. In most cases standard telecommunication infrastructures do not meet the long-term backup requirement during a power failure. It is for this reasons that large warning systems virtually always use two independent channels for siren network control. It is preferred to use at least one radio channel with its own backup infrastructure (Usually for 72 hours).