From Halopedia, the Halo wiki
Morse Code is a character encoding for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a given message. The short and long elements can be formed by sounds, marks or pulses, in on off keying and are commonly known as "dots" and "dashes" or "dits" and "dahs".
International Morse code is composed of five elements:
Morse code can be transmitted in a number of ways: originally as electrical pulses along a telegraph wire, but also as an audio tone, a radio signal with short and long tones, or as a mechanical or visual signal (e.g. a flashing light) using devices like an Aldis lamp or a heliograph. Morse code is transmitted using just two states (on and off) so it was an early form of a digital code. However, it is technically not binary, as the pause lengths are required to decode the information.
Morse Code is still one of many different codes still in use with the UNSC by at least 2552. When inside the Sharpened Shield, after accidentally killing a Huragok, Lucy-B091 briefly pondered about communicating her apology to its colleague in Morse code.
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