Police Sirens, and introducing the Rumbler

There are a wide variety of sirens at the disposal of police. However, there is now a new type of siren being added to their repertoire:

Christened with a tantalizing name, the Rumbler, it sends out low, bone-rattling vibrations, so it is not only heard, but also felt. One has been tested on the streets of New York, but the jury is out on whether it is effective, offensive or terrifying.