Tens of thousands of sirens have sounded across Germany for the first time since the end of the cold war in a nationwide test designed to inform people about what to do in a catastrophe and to test the readiness of the emergency services.

The alarms were sounded at 11am, and the all-clear given 20 minutes later.

Efforts were made in advance to inform schools, care centres and asylum-seeker shelters amid concerns the sirens could cause panic or traumatise older people or refugees who might associate the sirens with war.

“We have a very unprepared population,” said Christoph Unger, president of the federal office for civil protection and disaster relief (BBK). “It’s not like during the cold war when you could find an explanation for the warning signals on the back of the Yellow Pages.”

As well as testing technical scope, the Warntag (Warning Day), which will take place every year on 10 September, aims to inform the public about what to do. A siren that changes its pitch with no interruption is a warning. A single tone lasting for one minute indicates the end of an emergency.

The warning was also sent out via push notifications on smart phones, over tannoys on vehicles travelling through towns and cities, and in messages displayed on digital billboards. However while the traditional technology appeared to work well, many of the digital notifications were unreliable.

Some messages reportedly failed to come through, the interruption of broadcasts did not work on every wave length, and delivery of messages via a warning app called Nina were patchy.

At the height of the cold war, there were about 86,000 sirens across Germany. The majority were dismantled during reunification in 1991 but they still exist in most cities. In Berlin, most alarm systems were dismantled in recent years after residents complained about the noise. Some regions, such as Saxony and Bavaria, reinstated sirens after heavy flooding in 2002.

“We are aware that it in part didn’t work,” a spokeswoman for the BBK said after the drill. “There were delays due to an overload of the modular warning system.”

She said the BBK would work on improving the systems. Its ultimate aim was to be able to trigger all systems at the press of a single button at the BBK’s headquarters in Bonn, and to deliver detailed information via the Nina app, such as evacuation routes.

The BBK said the alarm was available for a range of emergencies, from biochemical accidents to wildfires, floods, terrorist attacks and nuclear fallouts.

“I have goosebumps,” admitted Lotte, a 52-year-old postal delivery worker, on her round in Potsdam as the sirens sounded. “At the same time I feel reassured that the sirens still work. And it’s good to teach young people what to do in an emergency.”