Why Telephones Have The * And # Buttons?

Have you ever wondered why do telephones have the * and # buttons? Well, the answer may be more weird than you think: they were actually included in the keypad as extra buttons, just in case someone figured out a use for them!

Here’s the interesting story.

Back in the day, a normal touch-tone phone could make a total of seven tones. The way it worked was simple: the user pushed a button and it made a combination of two sounds. A microphone hooked to a computer listened for the sounds and was able to decode the number. Two tones together were used because it made it harder for the computer to mistake the sound of someone singing or some background noise. (the article continues after the ad)

By using a grid, seven tones could make twelve different sounds.

keypad

Since seven tones would make twelve sounds, AT&T figured they may as well put the extra buttons, just in case someone figured out a use for them! The use came almost 20 years later, in the 1980s when AT&T introduced a series of “star codes” that let the caller do things like call back the person who had just called (*69) as well as other services. The # button became useful for a generation of voice-mail systems that proclaimed, “To finish, press pound #.”

If you like what you read, then you will definitely love this one: Why The Keypad Arrangement Is Different For A Telephone And A Computer?

Source: SolidSignalBlog
Photo: MikeBird / Pixabay