According to New Scientist, the company filed a patent for technology that would emit a low-frequency sound from a horn on the shield used by law enforcement. But it's not the sound that would disperse crowds. New Scientist reports that the patent states the sound would resonate in the respiratory tract making it hard to breathe. The device's effect could range from uncomfortable to "temporary incapacitation" of subjects.
New Scientist has more:
Acoustic devices haven't seen wide adoption because their range is limited to a few tens of metres. The patent gets around this by introducing a "cohort mode" in which many shields are wirelessly networked so their output covers a wide area, like Roman legionaries locking their shields together. One shield acts as a master which controls the others, so that the acoustic beams combine effectively.
Sound technology to make crowds back down isn't exactly new. In the U.S. police have used sound cannons to deliver messages to Occupy Wall Street protesters and in other situations, but such technology has been used in the past to help disperse crowds.
This story has been updated since its original posting to correct an error.