Serbia has seen a growing protest movement since a train station canopy in the town of Novi Sad collapsed in November 2024, killing 15 people. The collapse was blamed on corruption by officials.

The largest protest against government corruption so far took place on Saturday, March 15, with at least 100,000 people taking to the streets of Belgrade.

Participants accuse the police of using a sonic weapon to dispel the crowds. 

Videos on social media show protestors quietly standing in the streets during a period of silence for the Novi Sad victims, when suddenly a whooshing sound is heard and people flee in a panic.

Serbia's interior ministry, as well as Serbian President Aleksandar Vucic deny the use of sonic weapons. But what exactly is a sound cannon, or sonic weapon, and what kind of damage can they do to people?

What are sonic weapons?

Sonic weapons such as Long Range Acoustic Devices (LRAD), or "sound cannon," are considered non-lethal weapons.

Instead of bullets, they fire sound waves, emitting extremely loud noises. Regular sound waves get weaker the farther you stand from the emission point.

But the acoustic signals from sound cannon can be heard loudly up to a kilometer (0.62 miles) away. That's because the sound waves are fired at a high-pressure rate.

The closer you are to a sonic weapon when it is fired, the stronger the pain you will experience.

LRAD are said to reach a maximum volume of 150 or 160 decibels. A fighter jet engine at take-off reaches around 130 decibels. A normal conversation takes place at roughly 60 decibels, while a crying baby can crack 80 or even 100 decibels.

What's considered too loud varies from person to person and also depends on the frequency of the sound. But on average, sounds higher than 90 or 100 decibels are uncomfortable to hearing people. And anything above 120 decibels causes pain.

Symptoms in people exposed to sonic weapons

With extremely loud noises, such as those from sonic weapons, the sound waves hit the eardrum at high pressure and can cause significant damage as a result.

The reflex reaction when exposed to this is to cover your ears. That's why sonic weapons are also known as "acoustic handcuffs" — your hands can no longer be used for anything else while you are covering your ears.

In addition to the immediate pain caused by sounds at or above 120 decibels, permanent hearing damage or tinnitus can also occur after short exposure.

And it's not just the ears that can be affected. Psychological damage can also occur because you suddenly become the victim of an "invisible" attack that you have no way of defending yourself against.

Sound waves hitting people at a high-pressure-rate can have fatal consequences: In the case of an extremely loud noise such as an explosion, the sound waves can rupture internal organs, including the lungs, in people within the immediate vicinity of the blast.

Where have sonic weapons been used?

Loud noises have been used in warfare for centuries.

For example, Native Americans in what is now the United States used war drums to communicate with each other over long distances and to intimidate or confuse the enemy.

In World War II, sounds were also used in psychological warfare: The Nazi Luftwaffe (air force) equipped its dive bombers with ram-air sirens that produced a loud wailing noise when the planes took a dive. This caused an increased sense of panic among those under attack on the ground.

More recently, LRAD have been used on freighters off the coast of Somalia to ward off pirates. Police in Greece used acoustic weapons in summer 2021 to prevent migrants from entering the country irregularly, and thus the EU, from Turkey. US police used LRAD to disperse crowds protesting the G20 summit in Pittsburgh in 2009.

Havana syndrome: Do LRAD always sound loud?

There have been rumors about the use of sonic weapons without audible sounds or with low-pitched sounds at a high frequency.

In 2016 and 2017, US diplomats in Cuba's capital Havana reported health problems such as hearing damage, vertigo and trouble sleeping. Some of the embassy employees suffered concussions and a complete loss of hearing, according to US authorities. Among their list of possible explanations was an attack with a new type of sonic weapon.

Later, similar symptoms also occurred among US diplomats in other places, such as Vienna and Berlin. Investigations into so-called "Havana syndrome" never came to a clear conclusion, but an attack with sonic weapons is now considered unlikely.

This article was originally published in German