In Founder's Day, The Founder's Council used it. John Gilbert activated it. When it's activated, the device makes a high frequency noise that only vampires can hear. Werewolves can also hear it, as Mayor Richard Lockwood and his son Tyler were also paralyzed by it (However at the time Tyler was far beyond the five block range driving in a car, perhaps miles from the device, suggesting strongly that werewolves have much better hearing than vampires) despite the fact that their werewolf genes were still inactive. Since both vampires and werewolves are weak against it, it is possible to also harm hybrids. It was mentioned by John Gilbert that it would work only once, and for only about five minutes. The noise it emanated was described by Stefan Salvatore as like needles being injected into his skull.
During the Founder's Day Celebration, when the fireworks started, the device was activated, causing all vampires within range to fall to the ground in pain. Police force injected all the exposed vampires with vervain and then dragged them into the basement of Grayson Gilbert's old building.
John Gilbert set the building on fire, killing all the vampires who wanted revenge on the town, along with Anna, daughter of Pearl, and Damon Salvatore. The mayor was also mistaken for a vampire and was put inside the basement to be burned to death. However, he was killed before that, when his neck was snapped by one of the vampires trapped in the basement. Damon fortunately escaped the building by the help of his younger brother (Stefan) and Bonnie Bennett.
It is supposed that Katherine returned right after the device was put into use, or she was not in the radius of action, since she was not affected by it. However, there is a possibility that she may not have been much affected by it, as she easily resisted Bonnie's pain infliction in The Return.