Popular Science Monthly/Volume 89/July 1916/Look Out Perhaps the Man You're Talking to Wears a Detectaphone

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Popular Science Monthly Look Out Perhaps the Man You're Talking to Wears a Detectaphone  (1916) 
From Popular Science Monthly/Volume 89/July 1916
 

Look Out! Perhaps the Man You're Talking to Wears a Detectaphone
The receiver is worn beneath the shirtfront and the graphophone is hooked on the belt

A PATENT has been issued to William Heymann, of Washington, D. C, on a device which records on a graphophone drum whispered conversations, without the speaker being aware of the fact.

The receiver, which is of the usual detectaphone type, is to be worn beneath the shirtfront, and the electric battery and cylinder of the recording graphophone are to be hooked to the wearer's belt. Release a wound-up clock-spring and the needle of the graphophone traces the zig-zags produced by the sound waves.