Warning signs will fill the air for a short time in the early afternoon of May 1st as the country's emergency sirens are tested in the annual drill, which always takes place on the first Wednesday of the fifth month.

The test will last about ten minutes before everyone carries on with their daily business – including Labour Day celebrations, with this year’s drill falling on May 1st.

The siren system, with a total of 1,078 sirens enabling them to be heard by about 80 percent of the Danish population, is operated by the Danish Emergency Management Agency (DEMA), part of the Ministry of Defence.

The sirens are fixed to buildings or poles in cities and urban areas with populations of over 1,000, although mobile sirens mounted on police cars can also be used in less populated areas.

DEMA also uses social media channels to keep the public informed.

The agency has also issued helpful information on what to do if you hear the alarm sounding a real emergency, however.

In the event of a major accident or a disaster, the police may decide to use the sirens. At the same, time an emergency message from police or other authorities will be broadcasted by national TV stations DR and TV2, DEMA explains via a fact sheet available through its website.

It's important not to call the emergency number 112 unless you or people are around your are in immediate danger — either during the drill or a real alarm. You may block real life-or-death calls from getting through, DEMA says.

Emergencies in which the sirens might be used can include the presence of chemical gases, radiation or hazardous smoke.

The sirens are able to warn the entire population, but can also be used regionally or locally to warn specific areas.

Two distinct sounds are given by the sirens.

The first siren, signal 1, signifies ‘go indoors'.

Signal 1's tone rises quickly and falls again slowly, lasting for 45 seconds. If you hear the signal, you should go indoors and listen to the radio or watch DR or TV2 for further information. It is also important to make sure others know how to react, DEMA says.

Signal 2, a long tone lasting 45 seconds, means ‘danger is over'. It is now safe to go back outside and “return to your daily chores”, according to DEMA's fact sheet.