Wiretap-Proof Telephone, 1966

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This scrambler kept private phone conversations safe from wiretappers and eavesdroppers. Fitted to an ordinary handset, it needed no electrical connection, has its own power source. To hear, a person needed an unscrambler coded identically. Delcon Division, Hewlett-Packard Co., Palo Alto, Calif., sold it for $275 in 1966.