OBSOLETE TECHNOLOGY: Semaphore

Sure, it’s pretty fast but it’s not terribly secure. That’s the problem with flag semaphore, which has been used as a simple communication system since about 1800. The idea is this: Someone stands on the deck of a ship with two flags, one in each hand. He then does a dance a little like a cheerleader, wagging the flags to specific locations to signify different letters. Here is a sailor spelling out “SMILE:”

It works, and it’s still taught and used today in case of communications failures. Semaphores can be seen for miles if you have a good telescope, they work in all sorts of weather and they aren’t dependent on electricity. Flags don’t need recharging.

The problem with semaphore is that there’s no security to it. Unless you invent your own code, your enemies can see the flags and decode them as well as your friends can. It’s one thing to signal “HOLE IN BOAT SINKING FAST” when you are looking for help, but if the enemy fleet knows they’ve all but sunk you that’s another whole thing.

Semaphore pops up in weird places, because it’s been a big part of our culture. Today’s “peace sign” is actually a combination of the semaphores for “N” and “D” (meaning “nuclear disarmament.) See, and you thought it was a chicken foot this whole time.

Semaphore in the modern world

Believe it or not, the basic idea of semaphore still exists today. Using simple signals for letters underlies pretty much everything in the world of computers. It’s also the basis for the touch-tone system used by every phone out there. A form of semaphore is also used in infrared remotes.

The term “semaphore,” which comes from ancient Greek words meaning “flag bearer” or something very similar, is still used in the world of computers as well. Wikipedia’s page is extremely confusing on the subject, but I’ll tell you how I understand it. It’s a very simple method of documenting numbers in a way that doesn’t mess everything up. It’s not the sort of thing that average people would need to worry about, but it’s very useful in the programming world.

Simple forms of communication like semaphore aren’t used much any more except in the case of emergencies. Today we rely on much more complex forms of communication. But remembering how we used to communicate is important, too. So, even though this article is part of the “Obsolete Technology” series, is it really obsolete? I’d make an argument that it isn’t.

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About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 10,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.