Back in the early 2000s, the Nokia 3310 was my very first mobile phone. Every time I got a text message, it played the same ringtone. I must’ve heard it a million times—and yet I never realized what it actually meant.

Recently, while researching sound design in interfaces and revisiting the early 2000s, I finally learned the meaning behind that sound.

If you listen to it again (video with sound attached), you’ll hear three short beeps, two long, then three short again. Yes, Sherlock, it’s Morse code:

. . . – – . . .

And it literally spells out SMS.

Looking back, I probably should’ve guessed it. I’ve heard the Morse code for SOS signal (. . . – – – . . .) in movies and TV shows plenty of times—just swap the “O” (three long beeps) for “M” (two long), and you’ve got SMS.