Sonic weapons are an emerging category of non-lethal but potentially dangerous weapons and a relatively recent addition to China’s gray zone arsenal. They can be used as a harassment tool; for destroying sensitive electro-optical sensors as an electronic warfare component; or as a weapon of psychological warfare. 

Much like optical weapons, sonic weapons are generally considered anti-personnel, non-lethal weapons, and are used to stop, discourage or punish an unwanted activity. The tactic consists of blasting another ship’s crew with one of many loud sounds in order to incapacitate them. Their use is a growing trend in South China Sea incidents, as it enables ships at sea to attack other vessels while avoiding severe or lasting damage to their equipment or personnel.

The use of long-range acoustic devices (LRAD) has been documented in at least one occasion on January 28th 2025, when the Philippine Coast Guard's BRP Cabra was targeted by such device--amplifying a siren--while challenging the presence of China Coast Guard 3103 off the coast of Zambales. 

Two other LRAD incidents also likely occurred during (1.) the 2014 confrontation with Vietnam, when China tried to forcefully deploy its Hai Yang Shi You 981 oil rig near Triton Island; and (2.) against Filipino vessels between October-December 2023, during the extended stand-off at Second Thomas Shoal. (In each case the incidents were initially referred to as "sonar" related, but context suggests this was likely a mistranslation of the word "sonic".)

Sonar has in fact been used as a weapon at least once, when it was deployed against HMAS Toowoomba's sailors off the coast of Japan in December 2023, causing minor injuries to the Australian ship's divers while they were attempting to untangle fishing nets from around the ship's propellers.

Loud sirens were also among the tactics used by the China Coast Guard during the dramatic June 17, 2024 confrontation with the Philippine Navy at Second Thomas Shoal.

While the employment of sonic weapons at sea has not yet led to significant injury or death in the South China Sea, their use in other places leading to “Havana syndrome” (dizziness, headaches, pain and cognitive problems) suggests that long-term harm may yet result.