Sirens! Nothing new. Ubiquitous on city streets. Even small towns have, to some degree, grown accustomed to their shrill warnings. That's kind of a problem! Enter the Rumbler. You literally feel it coming.
How? It's actually pretty easy, and it started with music. Coupled with the high shrill of a "normal" siren, the Rumbler adds in a low-frequency tone that's so potent it can penetrate car doors. Ariel Kaminer, writing for the New York Times:
Rumblers [...]achieve their striking effect with a low-frequency tone, in the range of 180 to 360 hertz (between the 33rd and the 46th key on a standard piano keyboard), which penetrates hard surfaces like car doors and windows better than a high tone does. When it is paired with the wail of a standard siren, the effect is hard to ignore - like the combination of a bagpipe's high chanter and low drone, or perhaps like a train whistle and the caboose that moves that whistle through space.
The Rumbler is 10 decibles quieter than a standard siren and has no noticeable impact on driver health, pedestrian's ears or unborn babies (Kaminer is pregnant, and did not spontaneously go into labour while listening). That doesn't mean things don't get weird though:
Hearing a Rumbler while standing on the street, I felt a slight tingle under my ribs; in Officer Gallagher's car, I felt a gentle reverberation on the seat.
If you visit New York, expect you ribs to be rumbled very soo. Roughly 5,000 of the NYPD's 8,000 cars will have the Rumbler installed in the very near future. [NYT]