Sirens will sound across Bulgaria at 11:00 on 1 October, but it's a drill, not a real threat, the interior ministry says.
Both national signals, "alarm" and "all clear", will sound, and voice messages will play along with them, the ministry says.
The sirens will go off in Sofia, Burgas, Varna, Kardzhali, Montana, Pazardzhik, Pleven, Plovdiv, Ruse, Smolyan, Vratsa and Stara Zagora, plus the main towns of those regions. Equipment will also switch on in parts of Vidin, Pernik and Yambol, in towns and villages within 30km of the Kozloduy nuclear plant, and in local warning systems hooked up to the national network.
The drill will test the equipment of the national early-warning system and help train the public, the ministry says.