Wiretap-proof telephone
This scrambler keeps private phone conversations safe from wiretappers and eavesdroppers. Fitted to an ordinary handset, it needs no electrical connection, has its own power source. To hear, a person needs an unscrambler coded identically. Delcon Division, Hewlett-Packard Co., Palo Alto, Calif., sells it for $275, keeps your name and code locked in its vault. (more)
Unsold units were later turned into platform shoes :)
Just kidding.