Science: Ultrasonic Alarm

A new kind of burglar alarm, just patented last week, has already put a crimp in the burglar business. Developed by Samuel Bagno and manufactured by the Alertronic Corp. of Long Island City, the Alertronic alarm has one or more "loudspeakers" that generate sound waves with a frequency of 19,000 cycles a sec. This is too high-pitched for normal human ears, whose upper limit is about 18,000 cycles a sec., so the office or bank protected by Alertronic seems silent to a burglar, although every cubic inch of its air is in rapid vibration.

The machine can hear its own racket, of...

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