Amid police warnings for protesters to stay off the streets or risk arrest last week, a distinctly different and piercing sound could be heard.

The loud beeps came from a long-range acoustic device, a piece of equipment that can shriek repetitive blasts of noise at a volume of up to 152 decibels.

The New York Police Department bought two of the devices in 2004, at $35,000 apiece, in preparation for the Republican National Convention in 2004. At the time, police officials said that they would be used only for announcements, and that their shrill deterrent function would not be employed.

But during the protests that followed a grand jury’s decision not to bring criminal charges in the death of Eric Garner after a confrontation with the police on Staten Island, the police activated the piercing beeps.