1. Introduction

The duty of the capital city of Prague is to ensure the warning of its residents, as one of the basic measures of the protection of citizens. This follows from Sec. 15 Act No. 239/2000 Coll. and Additional protocol to Geneva Conventions of 12th August 1949 article 61. The basic means of warning signals in the Czech Republic are alarm sirens.

Warning residents against imminent or incurred danger is one of the basic measures for their protection that is protection of health, life and property.

Endangering a part of the area of the capital of Prague (including a part of the monuments protection area) requires particular solutions in the field of warning citizens. In the capital of Prague, this includes particularities, where the following needs to be secured:

  • Selective warning, i.e. only in the area of the capital of Prague endangered by an emergency (e.g. industrial accidents), natural disasters (e.g. floods)
  • Propagation of warning signal in continuous city housing, where the warning signal must be immediately completed with emergency information.
  • Propagation of emergency information in public areas (streets etc.) and thus having the opportunity to influence the behaviour for example during evacuation.
  • Warning elements independent of electric energy supplies from central sources, as one of the first measures at imminent emergency or natural disaster is the disconnection of electric power supplies to the relevant area, among others for the sake of safety.

In the capital of Prague there is a Unified system of warning and notification run by the state, whose part is also a net of rotary sirens. The system meets the requirements of area coverage of the capital of Prague by warning signal, but from the viewpoint of solving warning in the area endangered by flood, it meets only partially the first given particularity.

Therefore it was necessary to realize an autonomous system of warning in Prague that would solve the needs of warning against danger connected with potential risks of:

  • Floods and related inundation and devastating effect of the break wave on the flow of the river Vltava. Floods and inundation from local streams, for example Berounka, Botič, Rokytka, ...
  • Dangerous materials from chemical, cold storage, pharmaceutics plants and other operations that deal with dangerous and explosive material escaping into the Vltava.
  • Road and rail accident when transporting chemical and explosive material
  • Air traffic accidents

and that even for 72 hours without electric energy supplies from central sources.

In order to meet these requirements the following technical-organizational measures were taken:

  • Building of electronic sirens capable not only of generating warning signals but also of transmitting verbal information and secure these functions for 72 hours without electric energy supplies from central sources
  • Using wireless (radio) connection to control the sirens and transmission of verbal information when the basic stations of that connection are placed outside the area endangered by flood and they are equipped by substitutive sources
  • Siren control and the possibility of information input is run from a workplace with permanent service - Operační středisko Krizového štábu hl. m. Prahy, OS KŠ HMP (Operational centre of Crisis management group of the capital of Prague), which is able to warn immediately - to provide information
  • Securing immediate information of television and radio broadcasting operators - OS KŠ HMP

The construction of electronic sirens of the system of warning the population of Prague started in 1997 and has gradually been extended in individual phases of sound distribution according to the degree of potential danger and financial means.

At present the warning signal in the area of the capital of Prague is broadcast by 408 sirens. From the given number, 244 pieces of electric sirens of full-area system of warning are part of the state property:

The system of warning and information in the property of the state includes 164 pieces of electronic sirens:

2. Structure and appliances

Autonomous system of warning and notification is built as a modular technically open system enabling continuous completing and extending, both from the point of view of the number of siren stations and also from the point of view of using information provided by them.

The system consists of:

  1. controlling workplace - Operational centre of Crisis management group of the capital of Prague
  2. electronic sirens with a controlling unit
  3. appliance for transmitting radio signal to control sirens and verbal information transfer

Controlling workplace of the system of population warning

Controlling workplace of the system of population warning of Operational centre of Crisis management group of the capital of Prague enables:

  • Generating warning signals and subsequent informing of the population about current situation by means of radio and television broadcasts, with which the capital of Prague has entered into a contract of cooperation
  • Connecting voice announcements recorded in advance (general warning, the danger of flood wave, chemical accident, radiation accident, fire alarm, sirens test, end of alarm) with electronic sirens
  • Connecting VKV broadcasting (radio CITY 93,7 MHz, possibly of public service radio),
  • Direct voice input from the Operational centre of Crisis management group of the capital of Prague, as additional information for the population


During floods in 2002 this was used for announcement of voluntary and subsequently compulsory evacuation in the premises of the Old Town, the Lesser Town, Karlín, Libeň and Holešovice. More than forty-thousand people were evacuated. It was proved in practise that the system of warning enabled not only to secure warning of residents but also their continuous informing, which significantly contributed to the smooth course of their evacuation without death and health tolls.

Electronic sirens:

Autonomous system of warning and informing in the property of the capital of Prague consists of 164 pieces of electronic sirens.

The siren control case with its equipment enables:

  • Controlling from the Operational centre of Crisis management group of the capital of Prague
  • Local activation of voice announcements recorded in advance
  • Direct voice input
  • Connecting VKV broadcasting
  • Operation from independent accumulators that enable independence of electric energy supply from central sources for 72 hours
  • State-wide remote control by warning system of selective radio signal

3. Warning signal

A decision made by the Minister of the Interior of the Czech Republic introduced one single warning signal in the area of the Czech Republic. This was launched on November 1st 2001 and the signal is called "General Warning".

That signal (General warning, electronic "speaking" siren; General warning, electronic rotary siren) is sent by a fluctuating tone for 140 seconds. The signal may be send three times in a row in three-minute-long intervals. It is sent in cases of endangering lives and health of inhabitants due to a natural disaster (earthquake, big earth slides), accidents with the escape of dangerous materials to the environment (accidents in chemical plants, in storage of chemicals or during traffic accidents, accident in nuclear energetic facility or other accident with the escape of radioactive material into the environment), or other extraordinary situations of larger extent (ecological accidents, large oil spills), flood waves and inundations.

The acoustic tone of the siren will be followed by emergency information for inhabitants about imminent or incurred emergency from mass media (of republic, regional, and local applicability).

4. Signal for calling fire brigade

Fire alarm is announced by an interrupted siren tone for one minute or by an interrupted signal in the form of 25 seconds of a continuous tone, a 10 second pause and then again 25 seconds of continuous tone.

It is signalled for the purpose of calling fire brigades. It is not used for warning the inhabitants!!!

5. Test of final elements of warning

Regulation number 380/202 Coll. of the Ministry of the Interior from 9th August 2002 about preparation and execution of tasks to protect the population, states that from 1st October 2002 the serviceability of unified system of warning and notification of the population will be tested every first Wednesday of the month at 12:00 p.m. It is carried out by the test of final elements of warning: Testing tone.