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JR writes in -

I thought this was a cool story that didn’t get wide pickup. I like #9 especially: IBM SELECTRIC TYPEWRITER… Because the Selectric coupled a motor to a mechanical assembly, pressing different keys caused the motor to draw different amounts of current specific to each key. By closely measuring the current used by the typewriter, it was possible to determine what was being typed on the machine. To prevent such measurements, State Department Selectric typewriters were equipped with parts that masked the messages being typed.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.



  1. Fredex says:

    This sort of thing comes under the heading of TEMPEST (Transient Electromagnetic Pulse Emanation Standard) which sets standards for RF emmissions from electronic equipment.

    Computer terminals and monitors have similar problems in that they emit RF while writing to the screen that varies with whatever is being painted on those pixels.