Countries develop Sonic Weapons, the silent weapons used in counter-terrorist and crowd control settings

Sonic weapons employ extremely high-power sound waves  to disrupt or destroy the eardrums of a target and cause severe pain or disorientation. This is usually sufficient to incapacitate a person. Less powerful sound waves can cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has occurred both in counter-terrorist and crowd control settings.