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Tones as means of user interface were invented in 1908:
Invented by engineer August Kruckow, the dial tone was first used in 1908 in Hildesheim, Germany
Note that in Europe, call progress tones are single-frequency, and ringing and busy tones are effectively series of beeps of different duration.
While Wikipedia does not give an exact date for the ...
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A beep is a fixed frequency signal generated by one of the most simple electronics possible. It predates for sure any more complex electronic sound. So the answer may be: It was used as soon as electronic generation was deemed more appropriate than using a physical bell. As such any reasoning is quite independent of computer usage, much like Leo's example ...
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