The service ability of unified system of warning and notification of the population is tested every first Wednesday of the month at 12:00 p.m. The sirens are used for general warning and fire alarm. In the Czech Republic the warning system is covering nearly 100% of all residential areas of our country. During floods in 2002 in Prague 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.