Another device I just learned about is called the Inferno.

“Inferno uses four frequencies spread out over 2 to 5 kHz. The idea behind it is that unlike a regular siren, these particular frequencies have a uniquely disturbing effect on people (and presumably cats, dogs and any other living thing). At 123 dB, it’s loud, but not significantly louder than any other alarm system. The advantage, according to Dr. Goldman, is the combination of frequencies. The human ear just doesn’t like it.”

Read More here

Its interesting how the development of alot of these devices seems to be a response to piracy on the high seas.

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