Wiretap-Proof Telephone, 1966

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.