My guess is that the weapon that the government has developed is based on ultrasound. The effective range of such a weapon is unknown, but it could be substantial and is obviously designed to break up large demonstrations or riots.
Imagine that there was a crowd that a government wanted to disperse... The weapon would be mounted on a tank-like vehicle. They would activate the weapon from a relatively safe distance, then drive the weapon into the crowd.
If you were a member of the crowd, you might never see the tank until too late, and you wouldn't see any kind of weapon, but the closer the tank got to you, the worse you would feel. Sick, nauseous, starting to lose your lunch and/or your bowel control... It could physically shake you, push you back, and incite your most basic emotions of fear and panic. At close ranges, it could also rupture your eardrums and damage soft tissue and internal organs, possibly even causing death.
Crowds of protesters would try to flee from the assault, though it is uncertain they would know where to flee to. As a result, crowds could panic, stampeding over people trying to get away. The media might change their approach for covering protests and uprisings, since they could also find themselves victims to such an assault. It is likely that such a weapon could damage expensive broadcasting equipment.
In short, it literally is a terrifying weapon.
Here is a relatively old article on focused energy weapons, many of which the government could be developing as we speak: